It looks pretty poor in sli, barely beating out 7950cf or gtx580sli. Could be down to early drivers.
It could be. But then it could be the memory bandwidth or some other bottleneck caused by the fact that this is a pretty weak spec card.
Without starting the argument again the 680 is very mildly specced. This is because it's clearly not a high end part. In gaming it performs amazingly, however, sooner or later with a mid ranged part you are going to come across some problems.
Honestly, if Nvidia really are pretending this is their high end card then they need help. Low memory bandwidth, pretty low memory for a £400+ card and so on all point the other way.
As for drivers? absolutely, it could well be that. But, Nvidia are usually much better at AMD with drivers. And they have had three months to work on them and improve them, and I imagine that that's exactly what they did.
Personally I would like to see unique non unified drivers. I am only too aware of problems when you try and mash everything all into one. Fix one thing, it breaks another (hobbyist programmer, worked with a friend on an emulator).
Let's say we fixed the payout code on one technology, that would then lead to the payout code becoming broken on another.
MAME is very similar. As they gleefully bolt on all these new techs they unknowingly break something else.