To test the power consumption of the test bench was plugged into a P3 Kill-A-Watt. Idle power consumption was taken 15 minutes after logging into Windows 7 with no other programs running. The load tests were done running FurMark 1.70 with a resolution of 1024x768. This brought the load on the GPU's to 100%.
One of the reasons the idle power consumption is so low is due to the fact that the card throttles back dramatically. The GPU core clock drops from 850MHz all the way to 157MHz and the GPU memory clock under load is 1200MHz and at idle is only 300MHz.
Benchmark Results: The total system power used while using the HIS Radeon HD5870 was surprisingly low for a card of this caliber.