I have absolutely no idea how you are coming up with the statement that it's not much more efficient than an undervolted 5970... lets say, being super, extra, double sugar on top generous, you can power a 5970 with 250w... that gives you ~750 MH/s. The BFL unit does 800 MH/s at 85w... that is 1/3 the power for more MH/s. In what world, exactly, is that "not much more efficient?"
UNDERVOLTED. 250W is at stock. Actually w/ memclock reduced it is less. I run 3x5790s. Full system 2.25 GH/s @ 870W AC (at the wall). So the idea that it is impossible is just stupid.
Undervolted 5970 can get 5MH/W
This statement is just laughable. You aren't getting a 5970 to spit out 750 MH/s for 150w... that is just a joke, right? Or are you, gasp, fudging your numbers to make them look legitimate, when they are, in reality, complete bullshit... just like you're accusing BFL of doing?
Your laughable. Please educate yourself.
https://bitcointalk.org/index.php?topic=58912.0More than one person has gotten >5MH/W with UNDERVOLTED 5870/5970. Notice the prefix "under" in undervolted as in voltage less than stock. Power consumption decreases by the SQUARE of the voltage reduction so a decent voltage reduction (say 15%) reduces power consumption by a significant amount (27% power reduction on a 15% voltage reduction).
Yes you can get >5MH/W on a 5870 or 5970. You can do the same thing w/ 7970, (and likely a 7990 also). Can you run it at stock clock? No and nobody said you could.
Before your start insulting people how about your a) READ and b) MAKE SURE YOUR ARE INFORMED.
Note I never said it the single "barely beats" a 5970. I don't undervolt. My electrical rates are cheap I simply experimented w/ 5970 to see if I COULD when the time came and 5970 reached end of life and difficulty increases made mining at stock voltage uneconomical.