Finding the 4x 3090 Sweet Spot

https://preview.redd.it/8o43bjhe9d1h1.png?width=5346&format=png&auto=webp&s=1c87c2ee8b8ffff43495f543266056b0e26d3947

In another post I had someone ask me about the power draw of the 4x 3090 setup so I'm sharing a a full test I conducted to understand the efficiency curve. Used this blog post (not mine) as a reference.

Setup:

• GPUs: 4x RTX 3090 (Dell OEM, EVGA XC3, 2x ASUS Strix)
• PCIe Topology: Gen 3 (Bifurcated: x16 / x8 / x8 / x4)
• Model: Qwen3.6-27B (FP16)
• Backend: vLLM v0.20.2 (TP=4)

Takeaways:

1. The 220W Sweet Spot: Peak efficiency (matches the blog's findings)
2. Diminishing Returns: Increasing the limit beyond 250W provides diminishing returns

Hope this helps someone. Happy to answer any questions.

I'm VERY satisfied with Qwen 3.6 27B as a daily driver, but I would still like to know if there are any better/bigger models I can run on this setup. My understanding is that the best I can do is DSv4 at Q2 - not sure if it's fully supported yet though.

Additional context: it's an open build on a generic mining frame. I'm cooling it with 10x TL-C12C-S (5 on each side of gpus perpendicularly). I finished building this very recently so I'm open to suggestions on how to improve it.