You should not miss anything when playing it on DX9, but if you get a chance to play it on DX10 you might [miss the fidelity when going back to DX9].

For DX10, we had to make bigger changes in our renderer. To utilize multi-core machines we identified good candidates, [such as] particle system and physics, and made them multi-threaded. It's normal development, but bugs are harder to track, performance is less predictable and there is no benefit for single core processors. So not to sacrifice single core performance, [development] needs to be done carefully and [performance] benchmarked often.

Via Next-Gen.biz