did you forget to enable AA piggus? I see a little bit of jaggedness in your screens
other then that yea I suppose its AMD optimized, those on nvidia are having major slowdowns right now with shadows on full, I had to set mine from Ultra to Very High just to stay about 40fps or better
edit: I just finished Bioshock Infinate, it was great all the way through but the ending was a mindfuck though, I was confused.
BTW if you guys didn't know yet, thier is a secret ultra hard mode in this game as well (1999 mode) here is how to unlock it
On the main menu, hit this key combination:
Up, Up, Down, Down, Left, Right, Left, Right, (Cancel), (Confirm)
its multiplatform too, works on console and PC, for PC users, hit whatever you have cancel and confirm set to in controls