The problem had been bugging me for ages. 8086k with a 1080Ti, I could get 60fps on a good day, or I could get 25fps, whether running 4k, 1080, low or highest detail. There should be no reason I was getting down to 25fps, especially when both my CPU and GPU were reporting around 20-25% usage. I had tried every suggestion under the sun, to no avail, and accidentally stumbled across the answer. A bad Displayport cable. You see, every other video cable is clock based - a pixel is sent once, and if a bad cable means it never gets there, you simply get artifacts. It doesn't impact your FPS. Displayport is different. It's a packetised transmission service. Which means if a packet doesn't get there, it can be resent. And if it's resent, that's less bandwidth to update frames more frequently. It's insane. I scoffed (in my head) at another forum member who said unplugging and replugging their video cable fixed the issue for them. Thought it was a coincidence and couldn't work. Well, I have to eat humble pie. If you have a high performance PC over Displayport where the components are idling, and you are getting bad frame rates, try a nice short and high quality DP cable, and make sure that there is at least 10cm between it and any power carrying cables. (To reduce electrical noise). Hope this post helps even one person, because the problem had me tearing my hair out.