Overclocking ur cpu can gain you about 1-5 more frames and will barely make in diffrent in video games( in cpu dependent games it can get you a few more, but theres really no real point in overclocking ur cpu,since its already more then good enough for every game, but its easy, so why not?)
the gpu is still the limiting factor in ur pc, and by overclocking it you can gain a big performence boost.
games today are very gpu intensive, you will probably want to change you gpu in about 2yrs, while ur cpu can last you more then 4 easily.(but that's all about personal prefrence).
i for example have a better gpu then you, with a worst cpu then yours, and i have no cpu bottleneck in any game.