It took nearly two weeks, but on December 7th, 2011 a patch was released for Batman: Arkham City that `fixed` DX11 performance, but only for those running 64-bit versions of Microsoft Windows. Those running 32-bit versions of the operating system will have to wait for another patch that will come at a future date. We played the game on the patch with various card and while single GPU gaming in DX11 mode on Batman: Arkham City has greatly improved we did still find some issues..."
Any major computer upgrade generally requires a full software reinstall too. No so if you heed the advice in the guide to Upgrading a Motherboard without Reinstalling. PCSTATS Tips