AMD's nifty ZeroCore Power feature confers an advantage to the Radeons when the display drops into power-save mode. Their fans stop spinning and their GPUs drop into a low-power state. Even when idle at the desktop with the display turned on, the second card in the 7970 CrossFire team stays in ZeroCore mode, keeping idle system power lower than the GTX 690's. Meanwhile, the Titan system draws less power when idling at the desktop than any other setup, which is quite the feat for such a large chip.
We tested power under load while running Skyrim, and we can do a rough estimate of power efficiency by correlating power draw and performance in this game, as our scatter plot does. The Titan-based test rig comes out looking pretty good overall.
Noise levels and GPU temperatures
At its default tuning, the Titan is true to its billing as quieter than a GeForce GTX 680. That's a very nice accomplishment, since we know it's drawing more power than the GTX 680 or the Radeon HD 7970, yet it dissipates that heat with less noise.
Speaking of the 7970, AMD's reference cards are much louder than is necessary. We've seen better acoustics from 7970 cards with similar performance and non-reference coolers, like the XFX Black Edition we tested here.