Heya MacPro 1.1 Users ! I just upgraded my ATI5770 graphic card to Nvidia Quadro K4000 with 3GB of ram. This card is smaller than my old ATI (only 1 slot) and has the same 6pin power cable only.
Working awesome ! 4K from my Lumix GH4 ? No problem ! Cuda rendering ? No problem. Maya viewport very fast !
But, first of all you need to upgrade your system to OSX 10.9
I recommend to use this very, very simply method: http://www.oemden.com
Cheers,
Dirk