I overclocked my GTX 650 from 1071mhz to 1100mhz using GPU Tweak. When I overclocked I did not change the voltage at all I left it at 1087mV will I need to change my voltage for the Overclock to be stable? (I have a 500w PSU)
Best way to answer this is to test it yourself. Start up a game or a benchmarking program and leave it on. If nothing crashes then you have a stable OC and there's no need to increase voltage.