NVIDIA GeForce 6800 Ultra Voltage Mod
 

Look for the chip at the back of the card as shown. You can measure the voltage of your 6800 ultra from the point shown below. Without drivers loaded it should be around 1.13v with drivers loaded it should be 1.43v. To increase voltage, you can solder a 100K variable resistor to the point shown.

http://www.vr-zone.com/?i=926&s=1