u/Big_Building9948

I am trying to figure out the best GPU setup for large-context agentic coding / local LLM work, and I am a bit stuck between raw compute, VRAM, bandwidth, and platform limitations.

My current system is:

• ASRock WRX80 Creator R2.0
• Threadripper Pro 5955WX
• 256 GB DDR4 ECC
• PCIe Gen 4 platform

My budget is roughly $6800 USD. I live in an EU country, so prices reflected are including VAT and tariffs; “just buy from the US” does not work in this case.

The options I am considering:

• 2 × RTX 5090: Around $6800 USD. Fastest option, but only 32 GB VRAM per card and no NVLink, so large contexts may spill to RAM/PCIe.
• 1 × RTX PRO 5000 Blackwell More VRAM, probably better for fitting larger models/contexts, but much less raw performance per dollar compared to 5090. ~$5900 USD
• 4 × RTX 3090 Interesting because of 24 GB per card and NVLink support between pairs, plus used prices are much better. But they are older, power-hungry, and I am unsure how practical this actually is for modern inference workloads.
• Other used workstation cards / mixed setups Open to suggestions, but RTX PRO 6000 Blackwell is not realistic. It is around $12,000 USD equivalent here, so completely outside the budget.

The main use case is agentic coding with very large contexts, ideally 256K–512K where possible.

I currently run what I would consider a pretty decent workstation/server setup:

• ASRock WRX80 Creator R2.0 motherboard
• AMD Ryzen Threadripper PRO 5955WX
• 8 x 32 GB Kingston Server Premier 3200MT/s DDR4 ECC
• 2 x 4 TB WD SN850x
• 1 x RTX 5090 (Founders Edition)

Since this platform is limited to PCIe Gen 4, I am wondering how much performance I would realistically gain by switching to a newer PCIe Gen 5 consumer platform.

Since DDR5 ECC is extremely expensive, moving to a newer workstation platform is not possible; so if I were to move, I would be looking at a consumer-grade setup instead, something like Z790, 13700K, with 4 × 48 GB DDR5 UDIMM RAM at around 5200 MHz.

I was also considering adding a second GPU to my existing WRX80 setup. However, if the GPUs would be heavily bandwidth-limited due to PCIe Gen 4, I am not sure whether adding another GPU would actually give me a meaningful performance gain.

So I am basically trying to decide between:

• Keeping the current WRX80/Threadripper Pro system and possibly adding a second GPU.
• Moving to a newer PCIe Gen 5 consumer platform for better single-GPU performance.

What would you do in my situation?