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 Vista desktop with the Aero theme enabled. The cards were tested under load running Left 4 Dead at 2560x1600 resolution, using the same settings we did for performance testing.
Recent GeForce cards have had some impressively low power consumption numbers at idle, and the GTS 250 continues that trend in surprising fashion, reducing power draw by 30W compared to the 9800 GTX+. That's with the exact same 55nm G92 graphics processor and twice the memory capacity of the 9800 GTX+, even. Power draw is also down by 15W under load, and in both scenarios, the GeForce GTS 250 consumes less power than the Radeon HD 4850 1GB.
That said, the reductions in power use aren't limited to the GeForces. Gigabyte's Radeon HD 4850 1GB also represents measurable progress versus the 4850 512MB.
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 GTS 250's noise levels, both when idling and running a game, are some of the best we've measured in this round of tests. The new GeForce would look even better, relatively speaking, were it not up against some very quiet but essentially broken Asus custom coolers on the Radeon HD 4850 512MB.
Meanwhile, the strangely high noise levels for the Gigabyte Radeon HD 4850 1GB card, which match at idle and under load, are not a fluke. Although Gigabyte chose a nice, powerful Zalman cooler for this card, they did not see fit to endow this cooler with intelligent fan speed control. Or even kind-of-dumb fan speed control. In fact, there's no fan speed control at all. When I asked Gigabyte why, the answer was: because this is an overclocked card. I wasn't aware that eking out an additional 20MHz required the total destruction of a product's acoustic profile, but that's what's happened here. And it's a real shame. A real, puzzling shame.
I used GPU-Z to log temperatures during our load testing. In the case of multi-GPU setups, I recorded temperatures on the primary card.
With that fan spinning at 100% no matter what, the 4850 1GB certainly has some nice, low GPU temperatures. Meanwhile, the GTS 250 is easily quieter, but still keeps its temperatures well in check.