ExtremeTech has written a guide on hacking graphics cards:
When Nvidia launched the 8800 GT, they told the press they left lots of headroom in the card, so card makers could, if they so desired, pump up clock rates and give buyers a little more value. Of course, that added value comes at an extra cost. As we noted in our recent 8800 GT roundup, the factory overclocked cards cost quite a bit more than the standard cards. These higher clock rates can make a big difference in some games, and less so in others.
Of course, you can simply take control of the situation by overclocking the card yourself. This article shows you just how to do that.