First off I know there are lots of RAM questions and that you will probably say "search!!!" Well I did and I couldn't find a clear answer so heres my quick and simple question. I have the first revision of the mac pro and I have the stock 1 gig of ram (2x512). I am looking at getting either 2(2x1gig) or 4(2x2gig) from OWC. Now I know that you have to buy in pairs for max speed (if that's the right term). Does this mean I would be fine having in one ram riser 2 pairs of different sizes such as (2x512mb) and (2x2gig)? Thanks for all the help.