I've checked out this guide for Mac Pro RAM configuration: http://manuals.info.apple.com/en/MacPro_Early2008_MemoryDIMM_DIY.pdf But I'm going to be mixing and matching some sticks. They're all the same kind but I'm going to be using 4 x 2GB and 4 x 4 GB for a total of 24 GB of RAM. The guide suggests doing it in pairs but does it make a difference if the 4GB sticks are higher up in the hierarchy? Or should I place the 2GB sticks first? Thanks for the help.