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. We have a broader set of results here because we've included those from our Radeon HD 5970 review, which were themselves largely composed of data from our Radeon HD 5700-series review. Although we used older drivers for most of the cards in that review, we don't expect that to affect power consumption, noise, or GPU temperatures substantially.
Interestingly, while the Radeon HD 5670 has a smaller GPU, it draws a teeny bit more power than our factory "overclocked" GeForce GT 240. Still, this is a very close race.
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.
Under load, the Radeon HD 5670 is the quietest contestant in our test bench by far. (The Radeon HD 5870 has kept that crown in the idle test.) Meanwhile, the Zotac GeForce GT 240's fan seems to spin away at the same speed regardless of what you're doing with your computer, producing quite a bit more noise in the process.
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.
Ah, so those blissfully low load noise levels on the Radeon come with a trade-off. The 5670 sees its temperature shoot past the GeForce GT 240 and even the Radeon HD 5770 under load, settling at a toasty 71°C. We've seen far worse, though, especially from AMD's last generation of cards.