Power consumption
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 Half-Life 2 Episode Two at 2560x1600 resolution, using the same settings we did for performance testing.

The Radeon HD 4850's power consumption is lower than that of the GeForce 9800 GTX both at idle and under load. Interestingly, though, the card actually consumes more power than the GTX 200 series at idle.

GPU temperatures
Per your requests, we've added GPU temperature readings to our results. We captured these using AMD's Catalyst Control Center and Nvidia's nTune Monitor, so we're basically relying on the cards to report their temperatures properly. In the case of multi-GPU configs, we only got one number out of CCC. We used the highest of the numbers from the Nvidia monitoring app. These temperatures were recorded while running the "rthdribl" demo in a window. Windowed apps only seem to use one GPU, so it's possible the dual-GPU cards could get hotter with both GPUs in action. Hard to get a temperature reading if you can't see the monitoring app, though.

AMD's use of a single-slot cooler for the 4850 yields the highest load GPU temperatures of the lot. The GeForce 9800 GTX runs more than 25 degrees cooler.