Unsurprisingly, the HD 4870 X2 power consumption hasn’t changed much from the reference HD 4870 X2. At idle the system pulled 248w, at load it pulled 394w, and with the GPU overclocked it pulled 411w.
Temperatures, on the other hand, were completely different. At idle the cores were a cool 51 and 49 Celsius with the fan on auto fan speed. Under load the cores hit 65 and 62 Celsius, 20 Celsius lower than reference cards. Reseating the heatsinks with Arctic Silver Ceramique helped drop temperatures to 46 and 44 Celsius at idle and 64 and 59 Celsius at load. I believe the incredibly effective cooling of the cards was what helped me hit the 840MHz core, 1000MHz memory overclock with stock volts.
One thing I noticed while testing this card was an unusual tendency to ramp up the fan to 100% at random. Over the course of the four days I was playing with it I tried to track down what was causing this but I was unable to replicate the issue repeatedly. Here’s a short video showing what the fan sounds like and it actually spun up while I was recording. Note that the fan is actually incredibly silent at stock speeds; the camera was 6 inches away from the video card.