As far as I'm concerned, at this price, it really should be beating 2x GT in SLI. Sure, it's the fastest single slot card, but for someone who wants the best of the best in their PC, who sticks with one card anyway? I'd find it hard to recommend this because due to it's price I don't feel it fits into the market very well.
Oh well.
The card only has to be better than the competitors entry at the same price point. So if, pricewise, it is the same as 2x8800GT then yes it should offer the same (to be competitative) or better performance to be attractive to us buyers...but then I guess the single card approach does make it more attractive anyway to many without xfire or sli mobos