Hi, I'm trying to buy more RAM for my 2011 iMac (the new one), but I don't know exactly what I have to get. Is 4 tablets of 4Gb DDR3 SDRAM 1333Mhz the best I can get for my iMac? How many pins does it have to be? Should I put them all the same or can I keep the 2 2Gb that I have and only buy 2 of 4Gb each or will I have performance issues? Thanks for your help!