I have a dual-CPU Mac Pro 4,1 w/ 5,1 firmware. I am planning on upgrading the CPUs. What tips/tricks/information should I know before doing this? I have looked at a couple of sites explaining the process, but I'm still looking to gather information. If I screw up, a replacement tray/new CPUs may cost upwards of $600-800. One of the sites shows how an experienced person destroyed their CPU tray. I am especially concerned because I am replacing lidless CPUs with lidded CPUs. As someone who is relatively knowledgeable in computer hardware but has never replaced/removed/installed a CPU before, what should I know? Any help/comments/tips would be greatly appreciated.