Sadly, that is normal behaviour. A lot of newer games are getting very CPU heavy and you really need an i7 now if you want to game above 60FPS and take full advantage of a 144Hz display. Overclocking your i5 will help to an extent, but your only real option to really fix this problem is to get an i7. Either that, or give up on 144Hz and try pushing a higher resolution instead. The 1070 does well at 1440p and the 6600k isn't really a limiting factor at that resolution.