Currently deciding whether to get the 21.5 or the 27 inch iMac... Either I'll get the High end 21.5 or the base 27 I plan to use it for normal school work and some moderate gaming aka Battlefield 3, Assassin's creed 3 and so on. Will the 650M handle ok? Or should I go for the 660 in the 27? I'm hoping that the 21.5 has user upgradeable ram as well.. From what I saw in the teardowns it looks possible. Any opinions?