If you have a Geforce card (Any Geforce card)
You can hack the bios using a program called: Nvidia Bios Editor by Ray Adams
http://www.x-bios.3dgames.ru/index.php
His page is down at the moment but it will be up shortly.
Its a great program it allows you to modify other settings as well =)
I used it to hack my Gainward GF3 TI200 GS to 200/500 and also turned on Agp Fastwrites. I like hacking the bios over using the software
tweak because everytime you reboot you card goes back to default settings and as soon as you load windows it gets o/ced again, I don't
think thats good for the card. So I hack the bios and now no matter if I reboot or put the card in a diff system it will always be at the settings I set them too. Its perm like you bought it from a store =).
Just one tip: Use the software sliders to test how high your card can handle then make the changes perm with bios hack.
Good luck...