4.2GHz is a pretty mild OC for the FX 8000 series. With that cooler you could hit the FX 9590 clock speeds, 5GHz, easily. 4.2GHz will be fine. The PSU should be fine so long as you don't plan to add a second GPU then you might have to upgrade to a new PSU since the FX series is power hungry, especially when overclocked.