<< You need a little program called "Powerstrip". It is a tweak utility, that works with all major brand video cards, and allows you to change GPU core voltage and Memory voltage. Very useful. 🙂 >>
It changes the speed of the Core(gpu) and the ram. Not voltage. Would be cool it if did, really push it then🙂
Nshidia cards-there is a program called coolbits that firts nicely in the control panel for the drivers.
Radeon-Go to tweak 3d and there are a bunch of files there for overclocking and such.