The biggest problem I have with an i7 is that I can't have two of them on a motherboard. In any rendering scenario I'm familiar with (AE, C4D, Maya, Nuke) I want as much RAM and as many cores as I can fit into my budget/computer case.
The new Mac Pro was clearly not designed with that in mind. It's always been pay more and get less when buying Apple. Historically this has been especially true in unique form factor devices but I don't care what my computer looks like.