I don't much understand why people want higher framerates in CS:GO. Anything frames greater than your refresh rate are just discarded, they're written over in the frame buffer and never displayed.
Regarding overclocking, I'd try it with the cooler you already have. If you find you're in the upper 80's, you might try Noctua's NH-D14, it's ~$66 and will probably be considerably quieter and good for lowering your CPU ~10c over what you have. Noctua's D15 is better still, but I don't think it justifies another $25-30.