We measured total system power consumption at the wall socket using an our fancy new Yokogawa WT210 digital power meter. The monitor was plugged into a separate outlet, so its power draw was not part of our measurement. The cards were plugged into a motherboard on an open test bench.
The idle measurements were taken at the Windows desktop with the Aero theme enabled. The cards were tested under load running Left 4 Dead at a 1920x1200 resolution with 4X AA and 16X anisotropic filtering. We test power with Left 4 Dead because we've found that this game's fairly simple shaders tend to cause GPUs to draw quite a bit of power, so we think it's a solidly representative peak gaming workload.
Overall, the new GeForces look quite decent on power draw. Interestingly, the Radeon HD 5850 draws less power under load than either flavor of GTX 460, yet the slower Radeon HD 5830 draws more. There's a simple reason for that: the GPU on 5830 has more units disabled, but it also has a higher clock speed than the 5850. Higher clock frequencies increase power draw, and higher voltages are often required to reach them. With a larger board and higher clocks the 5830 isn't particularly efficient.
The GF104 looks like real progress for Nvidia. The GTX 460 1GB pulls less power at idle and under load than the GTX 465 or the GTX 260, yet it usually matches or outperforms them both.
We measured noise levels on our test system, sitting on an open test bench, using an Extech model 407738 digital sound level meter. The meter was mounted on a tripod approximately 8" from the test system at a height even with the top of the video card. We used the OSHA-standard weighting and speed for these measurements.
You can think of these noise level measurements much like our system power consumption tests, because the entire systems' noise levels were measured. Of course, noise levels will vary greatly in the real world along with the acoustic properties of the PC enclosure used, whether the enclosure provides adequate cooling to avoid a card's highest fan speeds, placement of the enclosure in the room, and a whole range of other variables. These results should give a reasonably good picture of comparative fan noise, though.
These results tell a couple of important stories. First, the difference in sound levels between the GTX 460 768MB and 1GB cards comes from that noisy blower on our Zotac review unit. Nvidia's reference cooler is much quieter, as are most other video cards. I should say that we also have a GTX 460 1GB reference card, and its noise levels are similar to the 768MB card'snice and quiet.
The only thing quieter under load, in fact, is XFX's custom cooler on its Radeon HD 5830, which is actually a very similar design.
We used GPU-Z to log temperatures during our load testing. We had to leave out the GTX 260, though, because it was reporting some obviously incorrect values.
Happily, with relatively low power draw, the reference GTX 460 cooler can remain quiet while keeping GPU temperatures in check.