In this situation I think the Mac is not a viable choice as 3D Studio is not available on the mac and although you can run windows using an emulator that would be a waste as you would have MAC OS, Emulator, Windows, 3D Studio all using Ram and CPU Cycles. The other problem is the MAC Pro comes with an ATI 2600 GPU which would not be up to 3D rendering. There is an option to add a 1.5GB Nvidia Quadro card but thats £1500 on top of the Mac and software cost.

Mac's are great for photoshop and final cut stuff but I think it would struggle in this case.