Hmmm, until we see it in action we can't comment on performance. Besides it'll be easily a year before anything decent comes out with dx 10 behind it (and no, crysis doesn't count). Takes time for people to test the capabilities and utilise all the functions available.

Expect all the upcoming games which in part utilise dx10 to have minor improvements over dx9 in terms of small visuals  and, most importantly, large performance benefits.