I'm looking to upgrade my 27" 2011 i5 6770m 512mb to a 6970m 2GB. This is entirely possible with the available Apple service part but I was thinking and would really love a detailed answer. Could I install a 6990m? I'm aware Apple don't supply a iMac with this card but i'm pretty sure I read somewhere that Lion has support for all Radeon 6 series cards (could be wrong) If it does support it without EFI flashing then great. If not could I perhaps use a flash from a 6990 desktop possibly Mac Pro card that somebody has done on here??? Really need some intelligent answers on this, not the usual 'You should have purchased the higher model anyway', 'You can't upgrade the graphics' and Seems like a lot of work for not much gain. Thank you.