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 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 2560x1600 resolution, using the same settings we did for performance testing.
Here's where having a newer, smaller, 40-nm design pays off. The 5700-series cards draw substantially less power under load than their price competitors, and they idle down to some very nice lows.
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.
The 5770 has a beefier cooler than the 5750, which allows it to create less fan noise at idle. When running a game, though, the 5770's higher power draw demands a little more fan powerand thus noise. Both 5700 cards are among the quietest under load, regardless.
The third-party cooler on our Gigabyte 4850 doesn't ramp down its fan speed at idle, by the way; that's why it's comparatively loud in that test.
For most of the cards, we used GPU-Z to log temperatures during our load testing. In the case of multi-GPU setups, we recorded temperatures on the primary card. However, GPU-Z didn't yet know what to do with the 5700- and 5800- series cards, so we had to resort to running a 3D program in a window while reading the temperature from the Overdrive section of AMD's Catalyst control panel.
AMD has tweaked its fan control algorithms to reduce GPU temperatures in its more recent products, and that leads to an 18° C drop in peak temperatures compared to the 4870.