Mac – Is the MacPro 5,1 single or dual socket

Short answer:

The lowest end Mac Pro that can be upgraded to a 2.93 12-core Westmere is the 2.66GHz 12-core Westmere.

Long answer:

The single socket Nehalem and Westmere Mac Pros literally have one socket. Aside from that, most of the lower end configs ship with a 1066MHz memory bus instead of a 1333MHz bus. In order to upgrade to a part that uses faster ram you will need to replace all your ram, and probably solder some resistors to change the clock multipliers on the board.

Without SMD soldering you will need to match the bus speed of the processor, which means if you have a 1066MHz memory interface the highest end part you will be able to install is are quad core 2.66GHz Xeon E5640s. There is also no guarantee the firmware will actually initialize it correctly, though odds are good that it will.

According to the tech specs, you should be able to use OS X Lion (10.7) with the following specs:

• Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor
• 2GB of memory
• OS X v10.6.6 or later (v10.6.8 recommended)
• 7GB of available space

That would suggest to me that you would need to get onto 10.6 (Snow Leopard) + all updates and then could get to OSX Lion (10.7).

Mountain Lion+ Specifies an "early 2008 Mac Pro or newer", yours appears to be the iteration just before that.