You just have to allow more than 75% memory to be allocated to the GPU by running sudo sysctl -w iogpu.wired_limit_mb=30720 (for a 30 GB limit in this case).
Thanks a ton! I'm running on GPU w/ Mixtral 8x Instruct Q4_K_M now. tok/sec is about 4x what CPU only was. (Now at 26 tok/sec or so).