Although it's not a large sample, I've noticed my Gigabyte cards use 5-10% less power than my MSI cards.  While it could be just coincidence, it's also possible that the Gigabyte cards have a more efficient VRM (faster MOSFETS, lower resistance inductors, etc).  Has anyone come across any video card reviews that test VRM efficiency?  I've found motherboard reviews that look at VRM efficiency, but couldn't find anything for video cards.