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.
It isn’t often we see a Fermi product draining less power than AMD hardware, but considering the GTX460 is a mid/high range board and the HD5870 is AMD’s single core flagship it is understandable. When gaming, the reduction is only around 5 watts, but under Furmark load this increases to 31 watts. Not a huge reduction, but clearly noticeable.