That would work AT LEAST on medium.
EDIT: Im of to school, i'll talk to you later, see if @Sir Ragealot can help you he is good too .
Either get a ATI Radeon 6970 (recommended) or get a Nvidia GTX 590.
I just got that game and I installed the latest Nvidia driver and got the same shuttering issue you have. Go back to driver 280.26 and it should work fine until you get a new pc. It does give you an annoying error message when you start the game tough, but its worth being able to play.
damn lot of ati nut huggers around here