I have some information that might be usefull towards some of you guys. I did a 2600Pro contest a while ago, and kicked the cards ass at 1140MHz core, 830MHz memory and 2.15V vcore rofl.
There's a way to booster-mod your card. Please note that this is a picture taken from the Peak 2600Pro 256MB card, and other brands may differ. It'll allows you to fuel the card with more then the default 75watts that your PCI-express slot deliveres :
You should measure out these points before doing this. It'll increase the amount of Amps your Motherboard can maximum deliver. It's really handy when your going at 1000MHz or higher.
You can also remove the original capacitors, and use ones with a higher value for a better stabilized voltage at higher frequencies.
That was my card, with still the original caps on the card. If your going to use a huge cooler be sure to check first wether you solder 'm on the above side or the other side, cause a vf900 would fit anymore after replacing them. I had to solder them on the back on the card (reverse the caps if your going todo

)
The following picture nicely demonstrates on how far i went on my card:
Boostermod, Voltmod, A vapochill and ofcourse some fresh tweak-spirit
Yep.. the pretesting. Only problem was after this testing the card went dead.
Nice MS-Dos cursor lol.
Keep in mind that ocíng beyond a GHz with the core is going to cause serious short-life-time issues with this card. I happend to reach up to 2.15V Vcore and a 1140MHz stable core. 1200MHz would really happend if that Vapochill, or whatever did'nt kill the card somehow. It would be 100% overclock.