Apple does not offer the peak speed CPU options in the Mac Pro. Shown in the table below is a slightly faster 6-core and a slightly faster 8-core CPUs. Due to Turbo Boost, the actual differences in speed are small.
These are not large bumps up over the stock CPUs, but the Mac Pro is such a big investment that eking out another 6-10% makes a lot of sense in the context of total system cost, particularly if the starting model is the 4-core and a down-the-road desire for 6 or 8 cores develops.
If the new Mac Pro has a socketed CPU (and Apple has not “locked down” the system somehow in EFI firmware), perhaps the low-end 4-core can be upgraded to a fast 8-core, which would be an appealing path down the road as CPU prices decline.
One never knows what those hard core elves over at OWC might be up to, given their CPU upgrade program for the prior model. But they’re taking one apart, which is the first step to investigating possible enhancements.
TPD of 150 watts vs 130 watts should be a non issue for any reasonable usage, and probably a non issue in any case with Apple likely over-engineering the cooling system.