Be sure to try the ik_llama.cpp fork. Basically, it specializes in MoE CPU offloading on Nvidia cards, and more efficient quantization types than mainline llama.cpp:

github.com/ikawrakow/ik_llama.cpp/

And see this repo for specific 3090 configs: github.com/noonghunna/club-3090

Honestly I should just write up my general setup in this community too.