Elite Bastards posted a review on the Sapphire Radeon HD 4770 512MB and CrossFire performance

At idle, our system when coupled with the Sapphire Radeon HD 4770 uses around 135 Watts of power, which increases to 170 Watts in a CrossFire configuration, almost identical to the power consumption of a single Radeon HD 4890. During video playback the Radeon HD 4890 actually uses slightly less power than our CrossFire setup, with a single Radeon HD 4770 board consuming a tad under 150 Watts.

Finally, rendering an intensive 3D rendering workload, a single Radeon HD 4770 in league with our Core i7 system uses 185 Watts, which rises to 258 Watts in a CrossFire configuration, less than the Radeon HD 4890's 275 Watt consumption under load.

Sapphire Radeon HD 4770 512MB and CrossFire performance review