The Radeons have a unique capability called ZeroCore power that allows them to spin down all of their fans and drop into a very low-power state whenever the display goes into power-save mode. That's why they tend to draw less power with the display off. At idle on the Windows desktop, only a few watts separate the Radeons and GeForces in the same class. During our real-world gaming workload in Skyrim, we have a split result: the 7950 draws less power than the GTX 760, but the 7970 out-draws the GTX 770. Again, none of the differences are terribly dramatic.
Noise levels and GPU temperatures
All of these cards use the default cooler from the GPU maker, and that last graph illustrates how AMD's coolers for the 7950 and 7970 aren't all that spiffy. By contrast, that GTX Titan-style cooler on the GeForce GTX 770 is blissfully quiet. I wish the same could be said for the GTX 760's puny reference cooler, which is just like the 660 Ti's. That cooler doesn't register too strongly on our decibel meter, but subjectively, it's worse than the numbers would seem to indicate. The 760's blower makes a rough sound that grates on my ears, and I find it hard to believe the smooth hiss of the Radeon HD 7990 somehow generates more decibels worth of noise.
Thing is, unless you're getting a 7990, Titan, or GTX 780, you're most likely not going to be buying a card with one of these reference coolers attached. Companies like Asus, Gigabyte, and Sapphre tend to use their own coolers instead, and the latest crop of heatpipe-laden heatsinks tends to perform very well, combining low noise levels with decent cooling. We may have to test a few of those next time around, but it just wasn't, uh, in the cards for today.