Just wanted to chime in on this. I just picked up a pair of Sapphire Radeon 7970 GPUs. I've overclocked them to 1125MHz. I'm using Diablo Miner for this run. My hash rate ranges between 1335 and 1340 MHash/s. Note that this is with dual GPU.

EDIT: I'll try and get power figures soon. I have a Kill-a-watt, I just gotta find it.

EDIT 2:

System Specifications:

Intel Core I7 960 @ 3.2 GHz
24 GB DDR3-1600
2 x Sapphire Radeon 7970
Corsair 750W PSU
WD 2TB Black HDD

Power Consumption in Watts w/ (MHash/s):

Idle: ~130W (0 MHash/s)
2 x 925 MHz: ~670W to ~680W (1104 MHash/s) - Power use increases as temps increase
2 x 1125 MHz: ~750W to ~790W (1345 MHash/s) - Power use increases as temps increase
Idle (with OC): ~130W (0 MHash/s)

I'm guessing that a slightly higher rated power supply with better efficiency might be called for on this one.