Steve Hullfish writing for ProVideo Coalition reviewing the Nvidia K5000 GPU for Mac:
So if I had to make a recommendation, I’d say that if you’re already running a Quadro 4000-level NVIDIA card, you’d really want to save energy and heat to move up to the Kepler architecture K5000. Performance gains would definitely be there, but I don’t know if the dollars per “horsepower” are really there with that jump. However, if you’re running an older or cheaper graphics card and are starting to utilize the Adobe CS6 stuff or are running Maya, maybe, then you could see some real performance gains that would definitely be worth the money.
So your high-end Mac Nvidia CUDA-based GPU's currently look like this (prices current as I write this, subject to change):
Nvidia K5000 - $1,725.99 (B&H Photo), 1,536 CUDA cores, 2 PCIe slots
Nvidia Quadro 4000 - $742.91 (Amazon), 256 CUDA cores, 1 PCIe slot
Nvidia Quadro FX 4800 - $688 (Amazon), 192 CUDA cores, 2 PCIe slots