If this runs under 600MHz core, then this product is a friggin waste of silicon. Why put it out there if you can achieve similar performance with a pair of 560s@900MHz and in the same power envelope no less. Unless of course your main purpose is to greatly stretch your profit margins and rip off your customers?
I bet this is also one of the reason EVGA and Galaxy put 460 cores in their dual solutions - they were simply denied to use proper 560s because they would step all over the 590's heels at almost half the price...
I hope I'm wrong but things are starting to smell very fishy...
A pair of 560s OCed:
"Subjective obtained GPU power consumption = ~ 298 Watts"
A 6990:
Notice how they both produce 102fps@19x12 in BC2. The only reason the 560 fall back at 25x16 is because of their 1GB memory buffer.
Edit: I'd use W1z's charts but he doesn't seem to have an overclocked sli review.