Like others, we are experiencing problems with Yosemite and the ATI video cards with C4D and OpenGL. Right now we are still using GT 120 and Radeon 4870 cards in our Mac Pro machines, and need to find a solution that will allow us to show shadows in the viewports without causing the whole system to take a dive. Right now, as long as we don't enable extra things such as shadows in the viewport, all is well. On top of that, we just purchased a few LG 34UM95 ultra-wide monitors and want to get all that we can out of them. In looking at the discontinued GTX 680 Mac edition cards they seem to support the higher resolutions required but top out at OpenGL 3.x. The current production Quadro 4000 and K5000 cards don't list the higher resolutions as supported and also seem to top out at OpenGL 3.x. Since Mavericks, OS X has had OpenGL 4.x support but I'm not even sure that C4D uses anything above OpenGL 2.x as Maxon's website states most any video cards that support OpenGL 2.x+ on their system requirements page. We are not using VRay or any 3rd party render engine that takes advantage of GPU processing at this time, though we may in the future if it becomes necessary, so we'd like to be prepared with whatever cards we invest in. We do use Adobe's CC suite including After Effects which I believe takes advantage of CUDA. As our machines do not have Thunderbolt we will be using the Display Port to connect the monitors. We are running Mac Pro 5,1 (2009 4,1 machines flashed to the 5,1 firmware) with dual 6-core Westmere processors and 32GB of 1333mhz RAM on Yosemite 10.10.3 with the latest C4D R16 revision. Thanks!