Hi there, I've also got the same cooler on a phenom X4 955 Black edition (125 watts). From experience I can tell you that there are better solutions, the cooler master hyper 212 plus which is only a fraction of the price of the kuhler 620 performs within a 1-2 degree difference. Temperature wise on my phenom is 28-32 degrees idle (dependent on room temperature) and does not go over 48 on load withe prime 95. SO if your overclocking will increase the cpus wattage by around 30 watts then you should be fine, if you plan on ramping up the voltage higher then I urge you to get a better cooler, maybe the H100 or a high end air cooler.
Case fans are not typically suggested for radiators as most send air in a cone, you want fans with high static pressure so they send air in a more linear path and a bit stronger, but the kuhler 620 comes with one radiator fan. In addition, in my experieces with radiators I find much better cpu cooling with fans on the radiator used as intake as you use colder air to move through the fins rather than exhausting the already hot air from the computer case. Best if you use a push-pull config with the radiator.