Hey all, I am looking online for used mac pro's from 2009. I am wondering how the whole upgrading CPU chips works. I understand the physical process of replacing chips but i am unclear about the max upgrade capability for a particular computer. Fore example If i get a 2.0gHz 2xdual core (for a total of 4 cores) can i upgrade that unit to a 12 core 3.33gHz? Are there limitations? What are they? What is the lowest start point i would have to go in order to be able to upgrade it to the highest possible upgrade. If there is a chart somewhere that shows potential cpu upgrade paths that would be great. Thanks for the help!