At the moment I have a hd 7850 2gb powercolor which can overclock from Core clock 860 to 1050 and memory clock from 1200 to 1450 in msi afterburner. I am also thinking about overclocking my processor Amd Phenom(tm) II X4 945 Processor from 3.00 to 3.3 or 3.5 if I can. At the moment I cant because I am using a 500 watt which is minimum requirement for my gpu but I am thinking about getting a 600-650 power supply for these overclocks. Im just wondering is it possible to overclock both and would I see a big difference in games like Bf4 which im currently getting only 25-35 fps sometimes even 20 and skyrim where i get 35-50 with all the mods I have on (150).
Depending on the application/game you may recieve a 0 - 20FPS increase from overclocking the GPU.
THe CPU is more often 0 - 10. I'm not too sure on the PSU requirements with the OC's though. (I went overboard with mine when I was first building, and made sure I could SLI and OC later which turned out o be sooner haha.)
I would recommend getting a higher wattage PSU if you want to overclock your CPU aswell.
Overclocking your CPU may give you a good performance boost in games, but it will depend on the game and whether or not your CPU is what is limiting your performance.
Some games are more CPU demanding and so will benefit more from an overclock.