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).
This is interesting to note. So as processes get smaller and smaller, power usage will fluctuate more and more widely based on temperature. All the more reason to have good cooling.