It is 88% efficient at full load. Detailed lab test
here. I have this psu currently pushing 2 5850s and a 5870. Will probably be adding another 5850 to it soon.
BTW, more bang for buck with
this psu. Has about the same watts on the 12v rail, and cheaper. Also has a 7 year warranty and is 87% efficient at full load. I have that psu pushing 3 5970s. Detailed lab test
here