At this point in time the GX2 is probably the best performance for anyone without an SLI/crossfireX board.
And I agree with hatman, there are reviews that show the gx2 beating 3 3780's.
I agree price will be lower with 3780's, but if you want a good price you can have my 4200ti for 50$ that's even better ;-)
Sure the card is far from perfect and it's just an SLI on one card, but it's still the fastest single card for someone with 1 PCIe slot.