NL_Bob_DTC thank you for posting the screenshots.
I was worried the CPU might be holding back the framerate, but that's not the case.
The green GPU line is right next to the yellow CPU line in the performance graph. Both are rendering frames at an average of 5-6ms.
This means the GPU is maxed out and can't render frames any faster. If the GPU wasn't maxed out you would see the green GPU line below the yellow CPU line in the performance graph.
1000ms ÷ 6ms = 166fps
There's 1000 milliseconds in a second.
Despite the GPU only showing 54% utilization in your screenshot post below, there's a component inside the GPU that's being maxed out. My guess is the VRAM memory bandwidth is maxed out.
I play with graphics set to low on everything except for the first 4 settings (texture x2, mesh and terrain all on high).
I'm not sure what texture x2 means. Is that texture filtering? That might be causing the VRAM bandwidth to max out. Try lowering the first 4 settings and see if the green GPU line drops below the yellow CPU line in the performance graph.