We recorded the system wattage at idle and load to see how different the power usage is for these cards. A Crysis benchmark run generates the load numbers.
Surprisingly, there's not a whole lot of difference. The Radeon HD 3850 and its GDDR3 memory peak at 23 W more than the AGP Radeon HD 4650 under load. The old Radeon X700 is pulling similar power usage numbers compared to the AGP Radeon HD 4650. While the Gigabyte GV-R465D2-1GI does seem to be the most frugal power user, it doesn't lead by much when compared to it's PCIe Radeon HD 4650 sibling.