The main aim of DX10, as I understand it, is to reduce the overhead and make it easier for a GPU to process the information therefore any DX10 graphics card running a DX10 enabled game would do it faster than if it was running it in DX9L. It is just speculation until the DX10 games arrive but there have been slivers of evidence already. There was a story a while back of someone running a tech demo of Crysis in 2560x1600 on a single 8800GTX in Vista. The GTX is fast but it's not that fast, certainly not in DX9, but in DX10...?
All I was saying is that you can't compare these cards properly to the competition because they're the only ones that can run DX10 at the moment.