DX11 in this game is terribly broken. People with incredibly crazy rigs are getting massive stuttering while playing. For example, when I run the benchmark I'm getting highs of 70'ish FPS, but the stuttering drops the average down to about 19. With DX11 off (and everything else still set to high, including PhysX) I'm getting about 40 FPS average. Haven't really met anyone that hasn't had this issue yet.
Apparently 5 weeks was enough to pad console sales, lie to PC gamers that they were working on optimizing the game for the PC and going on holidays, but it wasn't enough to make sure that the game was actually optimized for the PC. Rocksteady can suck a dick.
UPDATE: Still no word on the patch but for anyone encountering DX9 issues also: disable PhysX. With PhysX on in DX9 I'm lucky to average about 36 fps. With it off, my fps jumps to nearly 70 fps. I'm going to wait until they fix this (since PhysX adds very noticeable visual effects) but if you don't mind missing out on them, just disable it the game runs fine with everything else maxed out (at least on a 560ti).