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. We measure results while gaming in Crysis Warhead and record the results.
This article is also worth a read if you own a GTX580 – GPUz can be used to disable power throttling.
Very similar power demands to the GTX580 AMP! we tested last week.