I had a chance to play with new Mac Pro recently.
It was a model with D700 GPU's and 64GB memory so was nice and powerful.
I wrote a short piece for the FCP.CO blog.
http://www.fcp.co/hardware-and-software/pro/1314-stressing-the-graphics-cards-in-the-new-mac-pro-with-vj-and-live-performance-tools