The current Mac Pro is long in the tooth and to all intents and purposes is dead, despite the so-called 'update' this summer. The Mac Pro forums are a pretty sad place, folk still clutching at straws, hoping something comes out next summer.
"Lloyd Chambers (MacPerformance Guide) thinks it may be August 2013 before Apple releases a new Mac Pro because of remarks Steve made two or three years ago, brought to his attention by a reader of his site, that Apple would not release a Mac Pro until USB 3 was natively supported. The Ivy Bridge Xeon is supposed to support USB 3 natively."
(http://forums.appleinsider.com/t/152825/future-of-mac-pro)
"Lloyd Chambers (MacPerformance Guide) thinks it may be August 2013 before Apple releases a new Mac Pro because of remarks Steve made two or three years ago, brought to his attention by a reader of his site, that Apple would not release a Mac Pro until USB 3 was natively supported. The Ivy Bridge Xeon is supposed to support USB 3 natively." (http://forums.appleinsider.com/t/152825/future-of-mac-pro)