From Apple:
Traditionally, pro computers have relied primarily on the CPU for their computing power. But as GPU performance has dramatically increased, software developers have begun to leverage that power in their apps. With the new Mac Pro, we looked ahead and engineered an even more powerful GPU architecture. Not only does it feature a state-of-the-art AMD FirePro workstation-class GPU with up to 6GB of dedicated VRAM it features two of them. With all that power, youll be able to do things like seamlessly edit full-resolution 4K video while simultaneously rendering effects in the background and still have enough power to connect up to three high-resolution 4K displays.
These won't do?
No, not if you use one of the majority of pro software programs that run on CUDA.
You just have 2 Very expensive graphics cards to drive GUI monitors while using external NVIDIA cards in expensive thunderbolt chassis along with pro video cards.