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Power consumption
We measured total system power consumption at the wall socket using a watt meter. 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, and cards were tested under load running Half-Life 2: Lost coast at 1600x1200 resolution with 16X anisotropic filtering and HDR lighting enabled.

Out of curiosity, I threw in a GeForce 6800 GT for these tests, because I wanted to see how the 6800 GS compared to its predecessor. Will the GS's smaller transistor count and newer fab process give it lower power consumption than the GT, or will the GS's higher clock speed offset its advantages?

The system with the 6800 GS card pulls about 16 fewer watts under load than the system equipped with a 6800 GT—not bad. The systems based on the two ATI cards require even less power under load, however. Also, notice that our idea of pairing up two 6800 GS cards to defeat a single high-end card has taken a hit. The SLI rig eats roughly 25 to 30W more power than a system with a single high-end GPU.

Noise levels
We used an Extech model 407727 digital sound level meter to measure the noise created (primarily) by the cooling fans on our two test systems. The meter's weightings were set to comply with OSHA standards, and the meter itself was mounted on a tripod approximately two feet from our test system.

I would be more confident in these numbers if the chipset fan on our Asus A8N-SLI mobo didn't rattle and clatter like it does sometimes. Still, the numbers here show the 6800 GS to be a reasonably quiet card by current standards, and that jibes with what my ears tell me. Two of 'em together in SLI make a lot of racket at idle, although they're comparable to a setup with one Radeon X1800 XL or XT under load.

The always-on, uber-loud fan on this Radeon X1600 XT has got to be an artifact caused by our review sample card's pre-production status. I hope. Please?