I recently bought a new graphics card (GTX 780Ti) for my MacPro (Mid 2010, OSX 10.10.1). If you are thinking about upgrading your graphics card, but are not sure if it will work on OSX, I can just tell you, that in my case it worked awesomely fine! And this is how I did it!
After having some concerns about the card getting enough power from the standard Mac PSU, turns out, it works like a charm! First grabbing and installing the last CUDA for Mac driver from the NVIDIA website. If everything worked fine, you can find the CUDA preferences at the bottom of your system preferences.
Make sure you have the right cables to feed your card with power! In my case there were two 6 to 6 pin PCI Express cables attached. But since the 780Ti requires 8 pin cables, it is necessary to get two 6 to 8 pin adaptors!
After those easy preparation steps, it was really just a plug and play thing! If you haven't replaced a graphics card on a MacPro before, here is a quick guiding vid I found online.
Since this Geforce GTX 780Ti isn't officially supported by Apple, the first grey start screen, with the Apple logo and the progress bar, won't show up anymore! Wich is because the graphics card doesn't start working until the system is running properly and the graphics card driver kicks in..:)
Another thing which stands out, is that the OSX identifies the card as NVIDIA Ashley, which wasn't a problem so far, since this is just an internal given name!
All recently tested GPU based functions (like TurbulenceFD simulation, GPU rendering with Octane for C4D) worked as expected!
An article about making GPU acceleration available for After Effects and Premiere CC 2014, will be released soon!
Let me be clear about this: The process I described in the article above, worked in my case as mentioned! If you decide to manipulate your device in a way which isn't supported by the manufacturer, you do it on your own risk! The authors liability is excluded in every case.