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.
Fantastic results for this platform, we measured around 8 watts at idle, and 17 watts when watching a movie. Under full load when gaming it was around 26 watts total.