My first 7970 came with a number of issues while booting. I had it RMA'd, the new card that just arrived reaches 750 MH/s (1225MHz core, 1375 ram, 1.07 V, 168A) with sensor readings (HWiNFO64) indicate I am pulling 193 watts (Core + RAM). My first card would already be over 220 watts at these settings, seems either software improved or hardware improved, I used the same drivers from the end of Feb, so probably hardware changed?
This is probably just from leakage. Each of the cards are going to have a GPU that is "binned" differently. I've found on my rigs that as soon as I let the temps go much further than 68C, power consumption starts climbing pretty heavily (additional leakage from heat). If I let the cards in one of my 4 card rigs run at 74-75C, power consumption goes up by almost 100W
at the wall. My 6970s/6870s/5870s/5970s don't do this until they get very hot (80C or above).