OS X 10.9 'Mavericks' — 64GB *NO GOOD* on 4/6-core Mac Pro
Bad news on using 64GB memory (4 X 16GB) on the 4/6-core 2010 Mac Pro. As per OWC:
Nope, still no go, can't even get the OS to load with 64GB in my 6-core.
Apparently a hardware limitation with the 4/6 core model processor tray/chipset