Built an 8× RTX 3090 monster… considering nuking it for 2× Pro 6000 Max-Q

I’ve been running an 8× RTX 3090 box on an EPYC 7003 with an ASUS ROMED8-2T and 512 GB DDR4-3200.

The setup is not pretty. Lots of PCIe risers, I didn’t know about MCIO 8 months ago. The board has 7× x16 Gen4 slots, so for the 8th GPU I’m using an x8/x8 bifurcator plus a daisy-chained riser: motherboard to riser to bifurcator to GPU 1 on the bifurcator and GPU 2 on another riser. This is purely because of physical space and riser length limits.

As expected, things are weird. One GPU runs at x8, the other at x4, likely the daisy-chained riser but I haven’t had time to deep-debug. Another GPU shows up as x8 even when it shouldn’t, either a jumper I’m missing or a 3090 with a mining or modded vBIOS. Stability only became acceptable after forcing all PCIe slots to Gen3 Although I still see one of the x8 GPUs "faiiling off the PCI bus" (shows up as NA on nvtop) and leads me to reboot the server(10minutes to vllm readiness).

Because of this Frankenstein setup, I’m considering replacing the whole thing with 2× RTX Pro 6000 Max-Q, basically trading 8 riser-mounted 3090s for a clean dual-GPU build. This would triple the cost of the system. My 3090s were about $600 each, while the Max-Qs are quoted at about $8,300 each.

Putting elegance and some hit-or-miss stability gains aside, is there any real performance upside here?

Quick power-efficiency napkin math says it would take about 7.1 years of nonstop usage to break even compared to the 8×3090 setup. I could switch from AWQ to NVFP4 quantization. How much performance should I realistically expect for AI coding agents like Claude Code and OpenCode?

Would prefill latency improve in a meaningful way?

VRAM would be roughly the same today, with room to add 2 more GPUs later without risers and potentially double max VRAM. But is this even a good platform for FP8 coding models like MiniMax 2.1 or GLM 4.7?

Am I missing any real advantages here, or is this mostly an expensive way to clean up a messy but functional setup?