I know you can swap the video card in the 2009 i5/i7 iMacs but what is the fastest card that will fit? Just wondering if there is anything that fits and is faster than a 2GB 6970M. 4850 to 6970 is still nearly twice the performance but...
No, 6970M 2GB is the fasted you can get. Any cards other than Apple official models will not boot in the iMacs. This is a EFI limitation, no work-around.