According to a link I got from the Steam forums, those new drivers improve DX10 performance even more than DX9. And according to that same link, it appears to be the first game with better fps performance in DX10 than DX9, overall.
And finally, in a piece of good news for those of us with the Stusserbeast, it’s apparently the first game (maybe ever?) to fully exploit the power of quad-core processors. Game ON!