Depends on the game but at anything under 1440P Intel will have the performance lead for quite some time unless AMD can get their single core performance up quite a bit.
In Fortnight with a 1080 Ti at 1080P the 8700K takes a 20FPS lead over the 2700X and in various other games it's sometimes more and sometimes less, Depends on the engine, Rainbow 6 Siege sees the 8700K with a 32FPS advantage, In CSGO the 2700X gets 438 and the 8700K gets 519, I know at that point it's not really important but it shows CPU does matter at 1080P.
I'm lucky and have both CPU's and for 1080P high Hz gaming I wouldn't dream of using the 2700X, For a higher res yeah sure as then it's just GPU bound but not 1080P.
Thought all this was pretty well known ^_^