I know the 2010 Mac Pro machines support B1 stepping Xeons, but I was wondering if that was it? Would they support A0 stepping Xeons or D0 stepping Xeons as well?
As for the A0 stepping:
I had been browsing through the EVGA forums, and one of the threads had folks discussing loading an SR-2 motherboard with dual A0 stepping X5650 Xeon hex-core chips.
Too lazy to look ATM, but they're almost certainly Engineering Samples.