[panamajack]

From Tom's Hardware: Intel makes those. Westmere and Bloomfield are die/architecture revisions.

As far as the differences goes, Westmere is on 32nm where as Bloomfield/Nehalem is on 45nm. They are both on the same architecture. Only the manufacturing process differs. Generally, the 32nm CPUs should run cooler.

From Wikipedia: The architecture of the Nehalem was the basis of the i7, which was revised in 2011 as sandy bridge. The Westmere is a more recent CPU. Westmere-EP is the first six-core dual-socket processor from Intel, following the quad-core Bloomfield and Gainestown (a.k.a. Nehalem-EP) processors using the same LGA 1366 package, while the earlier Dunnington six-core processor is a Socket 604 based multi-socket processor. The CPUID extended model number is 44 (2Ch) and two product codes are used, 80613 for the UP desktop/server models and 80614 for the Xeon 5600-series DP server models. In some models, only four of the six cores are enabled.

If you were building your own Hackintosh, die revisions might have more significance. However, if you are shopping for an Apple Mac Pro, check out

www.everymac.com

You will find a comprehensive list of most of the retail products, including the incarnations of the Mac Pro. The speed of the processor is an easier way to figure what kind of performance you can expect.

The Hackintosh, user-built servers, or Frankenmacs, open up the possibility of overclocking, which is where you would want the coolest running CPU you could find.