To test power consumption today we are using a Keithley Integra unit and we measure power consumption from the VGA card inputs, not the system wide drain. The best way to get maximum load results is by using Furmark, and even though it is not indicative of a real world situation it shows the limits the card can theoretically demand. The ‘gaming’ results are measured when playing Crysis Warhead and is a more valuable result to take from this.
The power consumption of the HD6800 series is noticeably less than the GTX460. Comparing the reference GTX460 at 170 watt maximum load against the HD6870 and HD6850, we can see a 17 watt and 41 watt difference.Sapphire Radeon HD6850 and HD6870 Review,