Just wanted to put a final nail in the coffin on this...I currently have two 1gb modules in my 20" 2.16Ghz C2D iMac (the last white iMacs). From what I've read, if I add two 2gb modules, the system will only be able to access 3gb. Is this still correct? If it is correct, should I just install one 2gb module + one 1GB for a total of 3gb? Or should I go with matching pairs and install two 2gbs? How much of a speed difference will there be?