Sharp drop in FPS in games

I decided to overclock my FX 4300
Asus m5a78l-le
Asus GTX 650 Ti
Power supply 500W
I overclocked it to 4500 Hz at a voltage of 1.43 V.
I tested it, everything seems to be fine, but I ran into such a problem in the Counter-strike Global offencive game, during the time of skirmishes from 250 fps drops sharply to 30-50, and at the end of the skirmishes, the fps resumes. I noticed that the multiplier jumps, as if there is not enough power. I turned off energy saving in the BIOS .. but I could not see something.