At idle, GeForce GTX 670 is just 1 W of system power behind AMD’s efficient Radeon HD 7950, and just 1 W ahead of the GeForce GTX 680. The older Fermi-based GeForce GTX 580 uses an additional 13 W, and the dual-GPU boards are significantly more power-hungry, even when they aren’t doing anything.
AMD’s ZeroCore suite of technologies enables additional savings once our host machine’s operating system puts its attached display to sleep. Shaving off more than 10 W gives both of the Radeon HD 7900-series cards a lead here, while the GeForce GTX 670 and 680 shed very little power at all.
Nvidia claims a typical board power of 141 W—about 30 W less than the GeForce GTX 680’s typical power rating. A quick run through 3DMark’s Deep Sea and Temple demos allows us to chart system power use, where we see the GeForce GTX 670 using slightly more power than AMD’s Radeon HD 7950, less than the GeForce GTX 680, and significantly less than a Radeon HD 7970. The GTX 580 is there to show that even AMD’s flagship is a more efficient choice than last generation’s most compelling options.
Averaging out system power use doesn’t yield worst-case consumption numbers, but it is a more realistic look at gaming over time.
Truly, the GeForce GTX 670 looks pretty sharp, using just slightly more power than Radeon HD 7950—a card it easily outperforms. The Radeon HD 7970 it closely competes against averages more than 50 W higher.
Though there isn't really a performance hit but it would be great to have seen the GTX 670 running at PCIe 3.0.
Nvidia has had a big lead in Dirt 3 and WoW for a very long time. This skews the results.
The GTX 670 is a fantastic card, don't get me wrong. Just pointing out that it's being slightly overrated here.