Performance scales dramatically on the CPU as you move towards about 4GHz because of how it distributes the load. The same goes for system memory as you approach the 10-12GB/sec transfer rate.

Until you can optimally fill the pipeline feeding your GPU, the GPU will be under utilized in this game. Need to get it tweaked on the front-side first, then tweak the GPU. You can verify this quite easily on an older system with a dual-core and older GPU's from 2012 and back. The game was originally designed to run on those systems after all.