You’ve made a fundamental error assuming that maxing out CPU and GPU automatically gives you the “sweet spot” where you are flickering between being GPU and main thread limited - this is absolutely what you want to achieve though. 
Unless you have perfectly balanced hardware, one of these components is going to be more efficient in the rendering pipeline than the other which creates the bottleneck, and the better you even this out without compromising the performance of the lowest common denominator the better the fps will be.