See, with windowed & borderless windowed, the game caps itself automatically at 60 so it can´t show the full potential of that issue since i normally play at 120-180fps and i think it could be some sort of software issue, since it not only happens to CS:GO but other games aswell, just not as dramatic. It´s fixes itself when i tab back in again even though i always was tabed in that game. If you are still interessted in the usage then here it is and it has less of an impact on gameplay when i only play "X" game. (borderless windowed).
EDIT: Also would like to add that i do not have a 80+ psu since its a prebuild
Als