Hello, I'm in the process of upgrading my Mac Pro 2009 4.1 to 5.1 with new CPUs and whatnot. I am also intending to upgrade to faster RAM (1333 Mhz) but there is something I am not sure about. According to Apple specs, RAM for MAC Pro 2009 should be ECC UDIMM (unregistered). However when I look at the specs of the Mac Pro 2010 (5.1) Apple suggests that both UDIMMs and RDIMMs (registered) can be used in that model. So my question is the following: can RDIMMs be used on a Mac Pro 2009 which has seen its firmware updated to 5.1 or am I stuck in using UDIMMs? Thank you.