You can only use up to 90gb for the GPU, so it doesn't fit

No. In Linux, you can ignore the BIOS (well, set it to 512MB) and set GTT to allow almost the entirety of memory for GPU. If you don't run a desktop GUI (and why would you), you don't need memory for much of anything else. Just a few GB for the OS and llama.cpp.

These are roughly the settings I use: https://github.com/kyuz0/amd-strix-halo-toolboxes#kernel-par...