@PointyJoystick
Is it possible to post a picture like the one I posted above? You can do it with Rivatuner. Or run hwmonitor, then enter the game and play for 5-10 minutes, then check the highest temperature of the cpu on hwmonitor.
If you are playing on a laptop, the processor speed may be throttling due to hot weather. Because if the fps does not increase even though you change the resolution, it means there is too much CPU bottleneck.
It's a fact that the game optimization was broken after Vol 5. It was fixed with 7.1.0, but it was never like in vol 5. I hope Vol 8 won't be worse.