According to HardMac, the new Mac Pro is due out March 16, and should sport a 3.33GHz hexacore processor. No one but Apple can say whether this rumor is accurate, but it’s consistent with the expected availability of the Intel i7-980X chip.
The Intel i7-980X is clocked at 3.33GHz with turbo boost to 3.6GHz. Apple currently charges a ~$1200 premium for a quad-core 3.33GHz Mac Pro Nehalem (see review), so it remains to be seen how pricing will pan out on the new model. Whether a dual-CPU dodecacore (12-core / 24 virtual core) Mac Pro will also emerge remains to be seen.
It appears that the new model is likely to use existing 1066MHz memory as in the current Mac Pro, a boon for anyone upgrading an existing Mac Pro Nehalem, since the memory can simply be moved into the new machine. That’s my best guess, not a fact. This is a huge savings if you’ve invested in 24GB, 32GB or 64GB of memory.
What new features the new model will have is also unclear. USB 3.0 is possible, but seems iffy at best. More memory slots or drive bays (or fewer) or better SSD support also remains to be seen.
Worth keeping in mind is that even if Apple does announce a new Mac Pro on March 16, availability in the past has been 1-6 weeks after announcement. Custom configurations generally take longer; stock ones take less time.
I plan on thoroughly testing the new Mac Pro as soon as I can obtain one.