We measured total system power consumption at the wall socket using an Extech power analyzer model 380803. The monitor was plugged into a separate outlet, so its power draw was not part of our measurement.
The idle measurements were taken at the Windows desktop. The cards were tested under load running Oblivion at 1920x1200 resolution with 16X anisotropic filtering. We loaded up the game and ran it in the same area where we did our performance testing.
The cards were measured on the same motherboard when possible, but we had to use a different board in order to run the Radeons in CrossFire, so keep that in mind. We even had to use a larger 1kW PSU for the HD 2900 XT CrossFire system, which will no doubt change overall system power consumption.
When running a game, though, the R600 does pull quite a bit of juice. The system with a single Radeon HD 2900 XT draws 48W more than the system with the souped-up GeForce 8800 GTS 320MB, and the 2900 XT CrossFire rig with its massive PSU sets what I believe is a new single-system power draw record for Damage Labs at 490W. That's a crown AMD's graphics division has stolen from its CPU guys, whose Quad FX platform reached over 460W. Think what would happen if the two could combine their powers.
Seriously, though, the 2900 XT's power draw is a strong clue as to why AMD elected not to pursue the overall performance crown.
Noise levels and cooling
We measured noise levels on our test systems, sitting on an open test bench, using an Extech model 407727 digital sound level meter. The meter was mounted on a tripod approximately 14" 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, including the Zalman CNPS9500 LED we used to cool the CPU. 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.