Are there any current Macs capable of running NVIDIA based CUDA SDK?
You could opt for an upgraded 6 or 12 core Intel Xeon 5690 3.46 GHz processor Mac Pro 5.1 and install a NVIDIA GTX 680 4GB graphics card running CUDA. 

That can be done relatively cheap compared to the trashcan Mac Pro price tag, and it would do the job beautifully.