Despite its portly Barts GPU, the Radeon HD 6790 isn't much of a power hog. Both of our GeForce GTX 550 Tis draw more juice under load—especially the 1000MHz Zotac variant.
Noise levels and GPU temperatures
I wouldn't pay too much attention to those noise and temperature numbers, for the simple reason that few (if any) retail Radeon HD 6790 graphics cards are likely to sport the same cooler as our engineering sample. Still, for what it's worth, the quicker Radeon HD 6850 ran cooler and quieter than the 6790 under load.