My refurbished Mac Pro is arriving this week. It has 3Gb of RAM. I want to add to that. I read that it uses 3 pieces of 1Gb RAM. Looking at the selection from OWC, it seems the 4Gb are the most affordable. I could get 3, so I had 12, or I could get 2, and then use 2 of the 1Gb, making a total of 10. Does that work, or is it violating some technical requirement? If you got 3 pieces of the 4Gb, could you run those with the last slot containing a 1Gb, or is that bad? Thank you.