It is being rumoured by ZDNet that Apple will release a new Mac Pro model this coming Tuesday with a new hexacore Core i7-980x processor. According to ZDNet the "tipsters" point towards Tuesday, March 16 as the likely date for the release.
The Core i7-980x is due for release from Intel this coming Tuesday and will mark Intel's first six-core processor running at 3.33GHz (TurboBoost to 3.6GHz) and based on 32nm technology.
9to5 Mac is speculating that the release will be tomorrow.