The Radeon HD 7790 actually draws a touch more power than the 7850 1GB at idle. However, it's substantially more power-efficient under load, where it doesn't consume much more than our reference-clocked Radeon HD 7770.
Noise levels and GPU temperatures
Sapphire's dual-fan cooler keeps the 7790 both quiet and very cool.
A note about our noise levels: I live on the eighth floor of a tall building, and it was unusually windy both times I tried to take noise readings for this review. I attempted to alleviate the problem by taking the lowest reading from a one-minute recording for each card at each setting, so occasional wind gusts shouldn't have impacted the numbers substantially. These cards really are all very quiet—except for the 7850, whose cooler whines a little more than the others under load. (I also heard a faint mechanical chirping from the 7850 and the GTX 650 that wasn't present on the 7790.)