I knew that raising the voltage makes your consumption go up exponentially, but this seems a lot. Have you measured your consumption at default speed/voltage? If i'm not mistaken it should be 256 with 900mV, but don't take my word on that.
Just did a quick test on my 4 boards:
256 Mhz, stock mV = ~160Gh/sec @ 235w (1.4w/Gh)
278 Mhz, 1380 mV = ~200Gh/sec @ 383w (1.9w/Gh)
Measured at the wall using a kil-o-watt. Power supply is Corsair AX860.
I know the firmware I am using is converting those clock and voltage numbers (as it thinks it is talking to an avalon board) but the overall Gh and power numbers are accurate.
Interesting! Thank you for the tests.