From TechARP, seems the first benchmark for performance under DX10 is going to be in Lost Planet, the PC port of the XBOX 360 phenom. ATI's a little grumpy because nVidia got the software ahead of time so they could optimize their drivers for performance with it, and ATI didn't. Gonna be a little funny to see the benchmarks, especially with the irony (as noted in the article) being that the game runs on ATI hardware on the XBOX 360.
Maybe you'd have gotten ahead of the ball a little bit, ATI, if you'd managed to put out some DX10 hardware before THIS WEEK? Hmm? You think? Gah.