I made a very specific edit that was apparently while you were searching for those. I said recent drivers. December 10&15 isn't exactly recent especially considering that the drivers specifically targeted for the 580/570 came out in January... Yes, AMD's drivers have improved as well, but the SLI scaling on the 500 series has been improving more than the drivers have done for single card setups.
Anyway, enjoy your Nvidia card. Whatever makes you happy.