TBH the 590 and 6990 are faster overall than both the 7970 and 680.
Nvidia will tell you whatever they want you to hear when they are selling something.
The irony is that the only reason the 680 would ever beat the 590 in anything would be because of drivers or poor SLI implementation.
I own a 7970 and it is overclocked. My friend owns the same board, same cpu same ram and same SSD I do and his 480 SLI have beaten my card in absolutely everything we have compared them in. For example with my GPU overclocked to 1125mhz I score high 8000s in P score in 3dmark 11. He hasn't even overclocked his cards (he wouldn't know how) and he scores high 9000s.
I'm not saying I would have a SLI setup over a single card (and I wouldn't, I'm not a huge fan of dual GPUs) but the 680 is not faster than a 590 IMO, not by a long chalk.
It's cooler, quieter, doesn't make the national power grid whine and won't cook your insides, but it isn't faster.
For your reference a 590 is pretty much 570 SLI. A 480 is just ahead of a 570 by a small amount and they are also clocked higher than the cores of a 590.
So IMO SLI 480 are quicker than a 590 if anything.
