Setup advice for 5090, 4090 & 2080ti to get them all working for person software development

Need some tips/ideas on getting the most out of my gaming systems. Turns out the old “junkers” I didn’t want to sell have come back to be useful. I’m a software dev, but doing this as a hobbyist writing a game in Godot, more to learn about LLMs than to make a game. I learn best with a project.

Hardware:

64GB 6000Mhz 9800X3D + RTX 5090

32GB 3600Mhz 5900x + RTX 4090

32GB 3200Mhz 3900 + RTX 2080ti

Right now I’d call my configuration basic, running Qwen 3.8 27b nvfp4 for 5090 (200k Context, full KV with MTPx4 & Vision, xhigh) [Bazzite + distro container for llama.cpp]. I’m trying to move my gaming to Linux. It’s the workhorse. The 4090 Q4_K_M (256k KV q_8 mid [not sure its active though]), also my Dev IDE: Godot, Deepseek Harness (used to be OpenCode), VSCode and random python harnesses (basic stuff like RAG and other AI type side projects).

The 2080ti is unused. But feel I’m leaving compute on the table, wondering if there is anything productive it could be doing? Should I swap it to be my dev box, then use it as a small code predictor LLM. 4090 becoming dedicated LLM?

My perceived issue is a single threaded methodology, one problem at a time either the 5090 is running or the 4090 is running not both. No idea how to go about getting a multi agent setup to have the both working well together, while still feeling like I’m in control. Maybe that is something I need to give up for better utilization.

Should I switch up the harness? I’m convinced 50% of good AI output is down to a good harness. But not sure what would be better to unlock parallel tasking.