# Dual RTX 3060 (24GB) vs Single RTX 3090 (24GB) for 32B Local AI

> **Direct Hardware Verdict**: Even though two used RTX 3060 12GB cards (~$440 total) undercut a single ~$680 used RTX 3090 by $240, a single unified 24GB GPU wins cleanly for builders. Under standard layer splitting, Dual RTX 3060s stream 32B weights at 360 GB/s (~13 tok/s), whereas the RTX 3090 pushes 936 GB/s—2.6x higher bandwidth (~34 tok/s)—without dual-slot spacing headaches or motherboard bifurcation limits. Worse, ComfyUI diffusion pipelines cannot combine two 12GB cards into 24GB for Wan 2.1 video.

## Contender Specifications
| Metric | Dual NVIDIA RTX 3060 (24GB Split) | NVIDIA GeForce RTX 3090 (24GB) |
|---|---|---|
| VRAM Capacity | 24 GB GDDR6 (2x12GB PCIe Split) | 24 GB GDDR6X (Single Unified Pool) |
| Memory Bandwidth | 2x 192-bit (360 GB/s per GPU) | 384-bit (936 GB/s) |
| Typical Price | ~$440 (2x Used) / ~$540 (New) | ~$680 – $750 (Used) |
| Estimated Throughput | ~13 tok/s (32B Q4) / ~48 tok/s (30B-A3B) | ~34 tok/s (32B Q4) / ~95 tok/s (30B-A3B) |

## Comparative Model Compatibility Matrix
| Model & Quantization | VRAM Demand | Dual NVIDIA RTX 3060 | NVIDIA GeForce RTX 3090 |
|---|---|---|---|
| Qwen 2.5 Coder 32B (Q4_K_M, 8k) | 23.1 GB | Tight Split (~13 tok/s) | Runs Comfortably (~34 tok/s) |
| Google Gemma 4 31B (Q4_K_M, 8k) | 21.4 GB | Runs Split (~14 tok/s) | Runs Comfortably (~37 tok/s) |
| Alibaba Qwen3-Coder 30B-A3B (Q4_K_M) | 20.7 GB | Runs Split (~48 tok/s) | Runs Comfortably (~95 tok/s) |
| Alibaba Wan 2.1 14B 720p (Q4) | 18.2 GB | Fails Single-Card 12GB Limit | Runs Comfortably (+5.8GB Unified) |
| FLUX.1 [dev] (Q4 / NF4) | 15.5 GB | Requires CPU Offload (>12GB) | Runs Comfortably (+8.5GB Unified) |


## Silicon Architecture & Thermal Analysis
Both rigs total 24GB on paper, yet their internal silicon topology behaves very differently under real AI workloads. Pairing two GA106 boards isolates two 192-bit GDDR6 domains (360 GB/s each, zero NVLink fingers) across separate PCIe slots drawing 340W combined. Pipeline splitting (`-sm layer`) activates only one card while layers pass sequentially, capping dense 32B decode near single-card 360 GB/s speed; row tensor splitting (`-sm row`) hits PCIe latency barriers unless both slots wire x8 lanes cleanly. Conversely, the monolithic GA102 flagship aggregates 10,496 CUDA cores and twenty-four 1GB Micron GDDR6X chips onto one unified 384-bit 936 GB/s memory controller. Video diffusion models like Wan 2.1 14B Q4 (`18.15 GB`) or FLUX.1 [dev] reside untouched inside one contiguous address space, and a single RTX 3090 retains an NVLink bridge upgrade path to 48GB later.

## Tier 1 Free Software Optimization ($0)
Already running Dual RTX 3060 12GB cards? Pass `-sm row -ts 1,1 -fa on -ctk q8_0 -ctv q8_0` in `llama-server` to unlock cross-card matrix row parallelism on x8/x8 boards, or deploy sparse `Qwen3-Coder 30B-A3B` (`20.66 GB`) and offload overflow experts via `--n-cpu-moe` if PCIe slots bottleneck.

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## Verified Hardware & Cloud Pathways
- Shop Tested Used on eBay (~$220 ea) ↗: https://www.ebay.com/sch/i.html?_nkw=NVIDIA%20GeForce%20RTX%203060%2012GB%20GPU&LH_BIN=1&mkcid=1&mkrid=711-53200-19255-0&siteid=0&campid=5339245689&toolid=10001&mkevt=1&customid=gpugarden_programmatic_md (rel="noopener sponsored")
- Compare New Prime GPUs on Amazon (ASUS Dual GeForce RTX 5060 Ti 16GB GDDR7 OC): https://www.amazon.com/dp/B0F4DVKSZ4?tag=sparecables-20 (rel="noopener sponsored")
- Rig Essential — Thermal Grizzly PhaseSheet PTM: https://www.amazon.com/dp/B0DB84CQW6?tag=sparecables-20 (rel="noopener sponsored")
- Rig Essential — upHere GPU Anti-Sag Bracket: https://www.amazon.com/dp/B076GYL25H?tag=sparecables-20 (rel="noopener sponsored")
- Shop Tested Used on eBay (~$680) ↗: https://www.ebay.com/sch/i.html?_nkw=NVIDIA%20GeForce%20RTX%203090%2024GB%20GPU&LH_BIN=1&mkcid=1&mkrid=711-53200-19255-0&siteid=0&campid=5339245689&toolid=10001&mkevt=1&customid=gpugarden_programmatic_md (rel="noopener sponsored")
- Compare New Prime GPUs on Amazon (ASUS Dual GeForce RTX 5060 Ti 16GB GDDR7 OC): https://www.amazon.com/dp/B0F4DVKSZ4?tag=sparecables-20 (rel="noopener sponsored")
- Rig Essential — Thermal Grizzly PhaseSheet PTM: https://www.amazon.com/dp/B0DB84CQW6?tag=sparecables-20 (rel="noopener sponsored")
- Rig Essential — upHere GPU Anti-Sag Bracket: https://www.amazon.com/dp/B076GYL25H?tag=sparecables-20 (rel="noopener sponsored")
- Rent on RunPod: https://console.runpod.io/deploy?ref=ynypzu94 (rel="noopener sponsored")
- Rent on Vast.ai: https://cloud.vast.ai/?ref_id=723130 (rel="noopener sponsored")

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