Mac Pro Xeon CPU's always come out before the PC side gets them.
If PC's get them in March Apple will have them in February.
Xeon 51xx release date: June 26, 2006
Mac Pro 1,1 release date: August 7, 2006
Xeon 53xx release date: November 14, 2006
Mac Pro 2,1 release date: April 4, 2007
Xeon 54xx release date: November 11, 2007
Mac Pro 3,1 release date: January 8, 2008
Xeon 35xx and 55xx release date: March 30, 2009
Mac Pro 4,1 release date: March 3, 2009
Xeon 36xx and 56xx release date: March 16, 2010
Mac Pro 5,1 release date: July 27, 2010
Intel was manufacturing their boards for the 2006 -2008 systems, so they gave Apple preferential treatment in terms of pricing and availability dates (more money in board manufacturing than in the chips ).Hey! One out of five ain't bad