Hi, I'm just looking for some information regarding the memory configuration of a Mac Pro. I would like to buy one of these systems but because of the prohibitively high price of RAM, I'm goin to go with 2GB to start with and add later. I am aware that to get maximum performance, BOTH riser cards need to have some RAM installed to enable quad-channel mode, however: If I go with 2GB (Apple-installed), I will end up with 4x512MB. If I then buy a 2GB (2x1GB) pack from Crucial at some point in the future, will there be any loss of performance due to having 2x1GB on Riser card 1, and 4x512MB on Riser Card 2, or should I ideally go for 4x1GB (a much more costly option)? Many Thanks for your help, it's much appreciated.