boju :
Have my doubts about the 8600k even though it has 6 proper cores its deceiving. As this processor is popping up in more systems, I'm seeing more and more people complaining of high cpu usages on high Hz monitors. 4K 60Hz not so much an issue obviously because the cpu doesn't need to prepare so many frames. 1080p and 1440p gpus are able to produce a lot of frames and linearly the cpu usage goes up too. In this instance, Hyperthreading can help enormously.
Imo
8600k good for 4k 60Hz
8700/8700k better suited for 1080p/1440p 144Hz
High CPU usage when running a high refresh display is pretty much par for the course now, even on an i7. There are some newer titles where even on my 8700k running at 4.9GHz I do see high CPU usage eg. AC: Origins, Battlefield 1, Star Wars Battlefront II in larger multiplayer maps. It's not a bottleneck, but usage is high. Depending on what you are playing, the only way to guarantee low usage would be to go completely overkill and look at X299 or X399 platforms and 10+ core CPUs with HT/SMT. Even then, those chips tend to have weaker per core performance and can still cause bottlenecks because the game engines can't scale beyond maybe 12 threads right now.
I'd agree if you have a high refresh monitor, you probably should look at an i7 right now to avoid getting CPU limited as much as possible, though this isn't always avoidable, especially if you start shooting for 240FPS on some titles.