Best Multi-GPU LLM Workstation (2026): Skip Dual 5090s

Bottom Line

• Best for most people: two Radeon AI PRO R9700s. 64GB of VRAM for about $3,400-4,000 in GPUs. Each card draws 300W. The build runs on an ordinary 15A circuit.
• Best CUDA route on a budget: two used RTX 3090s. 48GB for about $3,000-3,200. It holds a dense 70B at Q4. It is hot and loud.
• Skip two RTX 5090s. The pair costs about $12,000-14,000 for 64GB. That is more per GB than a 96GB RTX PRO 6000, and it needs a 20A circuit.
• Workstation tier: RTX PRO 6000 Max-Q, one to four cards. 96GB and 300W per card. Two cards (192GB) run on AM5 and a 15A circuit. Four cards (384GB) need a Threadripper and a dedicated 20A circuit.
• Buy one big card before two small ones if the budget allows. One 96GB card has no split to manage.

Prices are US street prices as of October 2026. GPU prices move weekly this year. For the slot and lane detail behind every build, see Motherboard and CPU for a Multi-GPU LLM Rig.

The Three Builds

GPU board power is from the vendor. Wall watts are our estimate: GPU power plus about 200-250W for CPU and platform, divided by 90% PSU efficiency. This is the method from our electrical requirements page.

Model sizes are byte-exact Hugging Face file sizes, read 2026-10-23. They are weights only. Add KV cache and runtime overhead on top.

The line nobody else prints. At October 2026 prices, two RTX 5090s cost $187-218 per GB of VRAM (derived). One 96GB RTX PRO 6000 costs $156-188 per GB at its late-September retail price (derived). Both read memory at 1,792 GB/s. The 5090 pair gives you less memory, more cost per GB, 1,150W of GPU power instead of 300W, and an electrician’s visit.

Build 1: Two Used RTX 3090s (48GB)

The limit that decides it: heat and a shared circuit.

Two 3090s draw about 700W of GPU power. With the platform, the machine pulls about 1,055W at the wall (estimate). That is under the 1,440W continuous limit of a 15A circuit. It leaves about 385W for everything else on that breaker. Do not share the circuit with a space heater or a laser printer.

Every one of those watts becomes heat in the room: about 3,600 BTU/h at full load (derived, 1W = 3.412 BTU/h). Plan for airflow and noise.

What 48GB buys is one specific model class. Llama 3.3 70B at Q4_K_M is 39.60 GiB. It fits across two cards with room for modest context. It does not fit in 32GB. Our 48GB setup guide compares this build with single-card 48GB routes. Our dual 3090 vs 5090 page covers speed.

Used 3090s are not cheap any more. ResalePrices tracked 317 eBay listings at a $1,541 average on October 22, 2026. The fair range was $1,498-1,600, up 6.1% in 30 days. The “$700 used 3090” on older pages is a 2024 price. Check each card with our used 3090 checklist.

Build 2: Two R9700s, or Two RTX 5090s (64GB)

The limit that decides it: the circuit.

No single consumer card has 64GB, so this tier is two 32GB cards. You have two real choices.

Two Radeon AI PRO R9700s. AMD rates each card at 300W, 640 GB/s, PCIe 5.0 x16, with blower cooling. Blowers push heat out of the back of the case, which suits two cards side by side. GPU Poet tracked 8 listings from $1,850 in October 2026. The lowest daily average ranged from $1,683 to $2,016. A pair costs about $3,400-4,000. That is $53-63 per GB, now equal to or below two used 3090s ($62-67 per GB, derived). You get 16GB more VRAM, a warranty, and 300W less GPU power. You give up CUDA: you run llama.cpp on ROCm or Vulkan.

Two RTX 5090s. NVIDIA rates each card at 575W and 1,792 GB/s, and asks for a 1000W PSU for one card. GPU Poet tracked 92 listings from $6,987 in October 2026. The lowest daily average ranged from $5,986 to $6,932. A pair costs about $12,000-14,000.

The 5090 pair is the one build here that does not fit a 15A circuit. Two 575W cards plus the platform come to about 1,400W DC and about 1,555W at the wall (estimate). The 15A limit is 1,440W. You need a dedicated 20A circuit (1,920W). HomeGuide estimates $250-900 to install one.

The PSU is the second problem. 1,400W DC is above a 1200W supply’s rating. You can cap each card at about 475W with nvidia-smi -pl to stay inside 1200W (derived). Otherwise buy a supply that delivers more than 1,400W on 115V input. Many “1600W” units do not. The Seasonic PRIME TX-1600 is rated 1,300W on low-line power.

So when does the 5090 pair win? When you run CUDA-only software, serve many requests with vLLM tensor parallel, and the model fits in 64GB. Each 5090 has 2.8x the bandwidth of an R9700 (1,792 ÷ 640). For one person chatting with one model, a single 96GB card does the same job with no split.

What 64GB runs: Laguna S 2.1 at UD-IQ4_XS is 53.61 GiB and splits across both cards. gpt-oss 120B (MXFP4, 59.03 GiB) does not fit on the GPUs alone. Our 64GB model page explains the CPU offload. Our 64GB setup page compares eight routes to 64GB.

Build 3: RTX PRO 6000 Max-Q, One to Four Cards (96-384GB)

The limit that decides it: PCIe lanes at four cards, and the circuit.

NVIDIA lists the Max-Q at 96GB of GDDR7 with ECC, 1,792 GB/s, 300W, dual slot, active cooling. Its product page says it scales to four GPUs in one system, for 384GB. The Workstation Edition has the same memory and bandwidth at 600W. For inference, buy the Max-Q. Our Max-Q vs Workstation page has the full datasheet comparison.

One card (96GB) runs Qwen3.5-122B-A10B at UD-Q4_K_XL (71.74 GiB) with about 24 GiB left for context. It also runs Llama 3.3 70B at Q8_0 (69.83 GiB). See best local LLM for 96GB VRAM. It pulls about 555W at the wall (estimate).

Two cards (192GB) still fit an AM5 board in x8/x8 mode. AMD lists the Ryzen 9 9950X with 24 usable PCIe 5.0 lanes, 16 of them for graphics. Two cards at x8 use all 16. The build pulls about 945W at the wall (estimate), so it fits a 15A circuit. It runs Qwen3-235B-A22B at UD-Q4_K_XL (124.91 GiB) with room for context.

Four cards (384GB) leave AM5 behind. Four cards at x16 need 64 lanes. AMD lists Threadripper 9000 with 88 usable lanes (up to 80 PCIe 5.0). Threadripper PRO 9000 WX has 144 usable lanes (up to 128 PCIe 5.0). Four cards take eight slot widths. The machine pulls about 1,720-1,830W at the wall with a workstation CPU. That needs a dedicated 20A circuit. It is also past what one 1600W supply delivers on 120V. Our 4x Max-Q build page does the full arithmetic. At 384GB you can run Qwen3.5-397B-A17B at UD-Q4_K_XL (228.43 GiB).

Price is the hard part. Central Computer listed the Max-Q at $14,999.99 in stock and Newegg at $17,999.99 on 2026-09-30. GPU Poet tracked only 2 marketplace listings in October 2026, from $21,789. Treat $15,000-18,000 as the retail range, and expect marketplace sellers to ask more.

What to Buy

Best value, ROCm is fine with you: two XFX Radeon AI PRO R9700 32GB cards, an X870E board that documents x8/x8, and a 1000W-class PSU.

Need CUDA on a budget: two RTX 3090 24GB cards, tested one at a time. Pair them with a 1200W supply such as the MSI MAG A1200PLS 1200W. AVADirect listed it at $227.52 on 2026-10-23.

More than 64GB, or a machine for work: start with one RTX PRO 6000 Max-Q 96GB on an x8/x8 AM5 board. Add a second card later. Plan for Threadripper only if you will reach four.

The board for any two-card build: read the slot table before you buy. Two x16-length slots do not mean x8/x8. The motherboard and CPU guide shows which spec-sheet wording to look for.

Software: llama.cpp and Ollama split layers across GPUs by default. The cards do not need to match, and you do not need NVLink. vLLM tensor parallel splits every layer evenly, so it wants matched cards. See vLLM tensor parallel on two GPUs and is NVLink worth it.

When Multi-GPU Is the Wrong Answer

A second card buys capacity, not single-stream speed. In a layer split, the cards take turns. If one device holds your model, buy that device.

• One RTX PRO 6000 (96GB). More memory than any two consumer cards, one pool, 300W on the Max-Q, and no split to tune. It costs more than two 5090s ($15,000-18,000 against $12,000-14,000) and holds 50% more.
• A 128GB unified-memory box. A Strix Halo box (Ryzen AI Max+ 395) holds 128GB in one pool at about 256 GB/s. GMKtec listed the EVO-X2 128GB at $3,499.99 and Minisforum the MS-S1 MAX 128GB at $3,919 on 2026-10-23. That is about the price of two R9700s. It runs big MoE models slowly and dense 70B models very slowly. NVIDIA’s DGX Spark is the CUDA version; its price has changed several times this year, so check it on the day. Compare the boxes in which Strix Halo mini PC to buy.
• A Mac Studio M5 Ultra 256GB. $9,499 on apple.com (read 2026-10-22), with 1.2 TB/s of bandwidth. It holds Qwen3-235B-A22B at Q4 (124.91 GiB) in one quiet box on a normal outlet. It costs less than one RTX PRO 6000 and less than two 5090s. See Mac Studio vs RTX workstation.
• A prebuilt. If you do not want to manage parts, lanes and circuits, read prebuilt AI workstation vs DIY first.

Sources

• ResalePrices, used RTX 3090 eBay tracker: $1,541 average, $1,549 median, fair range $1,498-1,600, 317 listings, +6.1% in 30 days, updated 2026-10-22 (read 2026-10-23): resaleprices.com/gpu/nvidia-rtx-3090
• GPU Poet, RTX 5090 October 2026: 92 listings from $6,987; daily lowest average $5,986-6,932 (read 2026-10-23): gpupoet.com
• GPU Poet, Radeon AI PRO R9700 October 2026: 8 listings from $1,850; daily lowest average $1,683-2,016 (read 2026-10-23): gpupoet.com
• GPU Poet, RTX PRO 6000 Max-Q October 2026: 2 listings from $21,789 (read 2026-10-23): gpupoet.com
• RTX PRO 6000 retail: Central Computer $14,999.99 in stock, Newegg Max-Q $17,999.99, read 2026-09-30 (our price reference)
• NVIDIA RTX 5090 specs: 575W total graphics power, 1000W required system power, 32GB GDDR7, 512-bit: nvidia.com
• NVIDIA RTX PRO 6000 Max-Q: 300W, 96GB GDDR7 ECC, 1,792 GB/s, dual slot, scales to four GPUs: nvidia.com. Workstation Edition 600W: nvidia.com
• AMD Radeon AI PRO R9700: 300W total board power, 640 GB/s, PCIe 5.0 x16, blower cooling (Puget Systems parts listing and launch spec coverage, read 2026-10-23)
• RTX 3090: 350W board power, 936 GB/s (TechPowerUp)
• AMD Ryzen 9 9950X: 28 total / 24 usable PCIe 5.0 lanes, 170W: amd.com. Threadripper family table: PRO 148/144 lanes (up to 128 PCIe 5.0), non-PRO 92/88 (up to 80 PCIe 5.0): amd.com
• NEC 210.20(A) 125% continuous-load rule and the three-hour definition, via Mike Holt forum and electrician explainers; 1,440W and 1,920W are 12A and 16A at 120V
• Seasonic PRIME TX-1600: 1,300W on low-line input (Hardware Busters review, as cited on our electrical requirements page)
• MSI MAG A1200PLS: $227.52, AC input 100-240V, AVADirect (read 2026-10-23)
• llama.cpp server README: --split-mode default is layer (split layers and KV across GPUs, pipelined): github.com/ggml-org/llama.cpp
• vLLM parallelism docs: tensor parallel and pipeline parallel options: docs.vllm.ai
• Hugging Face file sizes, read 2026-10-23: unsloth/Llama-3.3-70B-Instruct-GGUF Q4_K_M 42,520,398,432 B and Q8_0 74,975,054,240 B; unsloth/Laguna-S-2.1-GGUF UD-IQ4_XS 57,566,704,320 B; ggml-org/gpt-oss-120b-GGUF MXFP4 63,387,346,208 B; unsloth/Qwen3.5-122B-A10B-GGUF UD-Q4_K_XL 77,029,996,032 B; unsloth/Qwen3-235B-A22B-GGUF UD-Q4_K_XL 134,123,851,136 B; unsloth/Qwen3.5-397B-A17B-GGUF UD-Q4_K_XL 245,272,148,448 B
• GMKtec EVO-X2 128GB $3,499.99 and Minisforum MS-S1 MAX 128GB $3,919, store product feeds (read 2026-10-23)
• Mac Studio M5 Ultra 256GB $9,499 and 1.2 TB/s, apple.com (our price reference, read 2026-10-22)
• Dedicated 20A circuit $250-900 installed, HomeGuide 2026 estimate
• CPU and platform watts, wall watts, BTU/h and cost per GB are our derivations and are marked as such

See Also

• Motherboard and CPU for a Multi-GPU LLM Rig — x8/x8 boards and the M.2 slot that steals GPU lanes
• Electrical Requirements for an AI Workstation — the 15A and 20A math behind the circuit row
• Dual RTX 3090 vs RTX 5090 — 48GB slow against 32GB fast
• Best 64GB VRAM Setup for Local LLMs — eight routes to 64GB, priced
• Can You Put Four RTX PRO 6000 Max-Q Cards in One Workstation? — the 384GB build in full
• RTX PRO 6000 Max-Q vs Workstation Edition — same memory, half the power
• What PSU Do You Need for a Local AI Rig? — transient spikes and the PSU ladder
• vLLM Tensor Parallel on Two GPUs — when to leave Ollama’s layer split