Not only is this card now cheaper than the 7970 (which is a good judgement of performance) (499 vs 549 USD)
Check this out...
Also, we can see some leaked benchmarks, (Tom's) here. This card is designed for 1080p resolutions, if you are going to be running anything higher AMD is the way to go. We still have yet to see formal overclocking performance figures, other than what I have posted earlier. It also seems Nvidia hurts more when AA or AF is being used.
Also it should be obvious that most of the games tested in the leak have a Nvidia Bias, except I am impressed with DIRT 3 results. The percent drop in performance with AA is generally higher than that of a 7970, and at 1080p you most probably will use max AA/AF/MSAA if you are dishing out this much money for a GPU. I dont understand why ultra or max graphics weren't used for Metro 2033.
The jump from a 6970 to a 7970 (price difference ~249 USD) is much larger than that of a gtx 580 to a 680 (price difference ~99 USD)
It doesn't look like there is a clear and obvious winner.