Pick up a GTX 570 2.5 or 670 and 680 with flashed EFI ROM.
The only card Apple offers is over priced Quadro, which is $800 on Amazon or $1200 from Apple.
I would like to move over to MACs from PC but use autocad and 3DStudio. The ATI radion graphics card HD5870 must be CUDA ready for 3D modeling, but the tech description at the online store doesn't confirm if it is CUDA ready.
CUDA is NVIDIA's parallel computing architecture. It enables dramatic increases in computing performance by harnessing the power of the GPU.
It is not offered by ATI/AMD Radeon cards.