The extent by which the GTX 480 bests the HD 5870 may be a bit of a surprise to those that expected the card to flop due to its reputed yield issues, but we're still surprised by how much the HD 5970 keeps its lead.
Nvidia is sure it's approach to the key DirectX 11 feature of tesselation is far superior to AMD's HD 5xxx series, the HD 5970 though manages to beat the GTX 480 in all the independent, tesselation-heavy benchmarks we used.
That card isn't even the equivalent of two HD 5870s either, being more akin to a twin HD 5850 instead. Still, it proves the GTX 480 is the fastest single-GPU card available right now.
Addendum: The Dirt 2 performance shown here is for the demo which runs in DX9 mode. In the he full release of the game (which does run in DX11 on Nvidia cards), it gets 52fps instead of the 67.5fps shown here.