The ultimate guide to overclocking

Free software – some of it official NVIDIA/ATI driver plug-ins – will do the trick from within Windows, and built-in safety cut-offs and stability tests make it incredibly hard to damage the card, though of course you are going beyond the warranty. It's also grown a little more complicated of late in that you may need to overclock the shader clock as well as the GPU and RAM for the best boosts.

In the case of NVIDIA cards, it used to be that this was twinned to the GPU speed, meaning a raise in one had a synchronous effect on the other, but for a little while now they've been able to be altered independently. So if you hit the speed ceiling on the GPU, it may yet be possible to eke more performance out of the card by pushing the shader clock a little further.