Overclocking?

I am running a I5 650 and was wondering if I should upgrade to a phenom II x4 965 and overclock it or should I just buy an after market cooler and overclock the I5. I also run a Gigabyte 7850 OC 1GB and was wondering if I overclock my current cpu (I5) or if I upgrade and overclock the phenom, and I overclock the 7850 more than the factory overclock would a Corsair cx600 be supply power? If so what kinda overclocks could I be looking at just for a generalization, I want to set a goal for myself and I know the 7850 is a overclocking beast. When I overclock my 7850 should I get a after market cooler and if so what would you recommend.