if you have the full blown 6800GT then there is nothing to unlock. Just get coolbits or riva turner and begin overclocking. You might want to flash the bios to ULTRA just to get a bit more volts on the gpu core, but it really depends on how well you can get an overclock. My 6800GT does like 430/1200 with the same cooler you got. It really depends on the card as to how far it will overclock. If you are really serious and know how to solder then you might check out volt modding.