At idle and during video playback, we see an increase of around 70 to 80 Watts in the move from a single board to dual Radeon HD 4870 X2 - Not too bad, although 300 Watts just for Blu-Ray playback in a CrossFireX setup is rather a scary thought.

If that seems bad, you might want to look away before taking in our 3D rendering performance numbers - Almost 400 Watts for a single Radeon HD 4870 X2 is hefty, but with two boards in tandem you're looking at closer to 700 Watts, with power consumption likely to rise even higher in situations where both CPU and GPU are being pushed hard by a modern game title. Ouch.