My system couldn't play the game well even without DX11 or physx but I thought it looked pretty great. But to answer the OPs question the performance you are getting is normal for that game. It is one of the very few games your card won't be able to max out at that resolution.
depends on the game. 4xaa/8xaf is the optimal choice. jaggies are still visible @ 2xaa.
Even if its there, its very minute.Not worth the performance drop by having more AA.I personally do not recommend AA at full HD or higher resolutions.4x AA is is recommended for resolutions below 1680x1050.