So I go the 27" 2.8Ghz Quad Core iMac. It came with the standard 4GB RAM. (2X2G) I know it has 4 slots in it, and is upgradeable to 16GB RAM. I am debating on buying 2x4G to bring my total to 12GB, and then I would have the option later to buy another 2x4G to up it to 16GB. My question is if I DO have 2x4 and 2x2, will my computer actually use all 12GB or will it retard the 2x4 down to 2x2 and virtually only use 8gb? I do a lot of video and photo editing, and I run parallels, so the more ram, the better. in short-- I can't afford 4x4 right now. So should I get 4x2 or 2x2 to add to my factory 2x2?