Last March, Intel released its Sandy Bridge Xeon, those expected for a future hypothetical update of the current Mac Pro. Such CPU are for the LGA 2011 socket. Current Mac Pro are based on the LGA 1366 socket (1366 connections). The difference is mostly linked to the parallel management of RAM modules (4 modules per CPU instead of 3 in LGA 1366). It also has a cost in term of design and production, so ultimately on the price of the hardware/workstations.
According to CPU World hereafter is the list of those new Xeon CPUs (clsesr to the Westmere powering current Mac Pro).
Apple has more than enough choice now to pick the Sandy Bridge Xeon CPUs it needs to finally deliver the new Mac Pro.