Faydon :
mainly 4:3 but i tried changing the resolution aswell but no difference
This is an aspect ratio, not a resolution.
What you are seeing as pretty normal. CSGO is a very old game that is built using a very old game engine, and as such, it is by no means GPU bound, which usually leaves one option, and that is to be CPU bound.
If you don't want to see your CPU usage so high in that game, limit it's frame rate. This imposes the effect of an artificial GPU bottleneck, and what you will see are lower temperatures and lower usage, as neither the CPU nor GPU are spending time to produce the extra, unnecessary frames.
300 FPS is useless, as you can't see or display that many frames, even if you tried. It isn't a matter of throwing money at the problem either. The solution would require a screen that could display all of the frames, and that screen doesn't exactly exist.
Whether you need 300 FPS in your game to feel like your experience is fluid, is up to you, and totally subjective. Since servers, which ultimately govern the mechanics of the game, aren't going to ever be that responsive for multiplayer games, at least not for the foreseeable future, I suspect 300 FPS is well beyond the point where any higher frame rate benefit takes place.