Need to see more benchmarks, the
benchmarks I saw (PCPer) at 2560x1600 had the HD 6990 winning by 10% across the board (except in 1 or 2 benchmarks) vs Nvidia GTX 590. On the other hand, it could be a lot different at surround resolutions. On the previously linked HardOCP, looks like Nvidia is only winning on Metro 2033 (well of course, the game has the "nvidia" advertising when you start it) and tied or losing on everything else.
Personally, I'm almost rooting for Nvidia here.. the ATI drivers I have for my 5970 are terrible, if I use anything newer than 9.x it causes my system to hang when playing games. 9.x has slightly worse performance and the occasional driver crash (without needing a reboot).