Well, you shouldnt try to overclock any hardware, i think. I guess you dont have the needed cooling flow, so it can really be dangerous for you hardware. Also, your OS could crash because of that.
50-90 FPS are not bad, but i cannot say anything more because you did not tell us your game you checked the fps in

And yep, its normal that your FPS claims to 190 or more if there is not much work for it.
With 25+ you shouldnt notice any bad smooth anymore.
Youre right, your CPU is a bit slow compared to your GPU.