The new systems will represent the first architectural overhaul to the Mac Pro family since Apple introduced the Intel-based Power Mac successor at its August 2006 Worldwide Developers Conference. They'll also be amongst the first machines from any PC manufacturer to employ chips from Intel's upcoming Penryn family of 45-nanometer (nm) microprocessors -- specifically the upcoming Hi-k Xeons, which will be available in dual- and quad-core variants for workstations with front-side bus speeds of either 1333MHz or 1600MHz.
AppleInsider's article is corroborated by an Inquirer report which claimed that Penryn processors were being bought up by Apple leaving very few in supply.
According to AppleInsider "the new Mac Pro line lineup will top out with an 8-core configuration that employs two top-of-the-line quad-core "Harpertown" chips. The top-bin Xeons, which offer the faster 1600MHz bus and 12MB of L2 cache, will start trickling in around mid-November at speeds of up to 3.2GHz."