I just bought a Mac Pro 3,1 to replace my old 1,1. It is a kicking computer, but only has half the memory of my old one (some slots open). Can I use my old 667mhz memory in the 3,1 (800mhz) alongside the 800mhz ram already in it? Can I use 667mhz RAM in it at all? It would just be temporary for a few months until I save up enough money to buy new 800mhz memory. Thanks!!