I just got a GTX 980 Ti and I have to say I am having some trouble. I installed it, boots off the web driver, but it is far from smooth. Mouse is jittery, floaty and sometimes like pushing mud. GPU programs like creative cloud eventually bog down. It's very hard to use in the yosemite interface. Put the GTX 680 back in and it's all normal.
Can't figure it out. 980 reports excellent render times in Blender and Cuda-z, but it doesn't seem to be working to it's full potential on the Mac UI. Thought it was maybe drivers, but then saw that others were using it just fine. It reports in system profiler as "nvidia graphic device" and in photoshop shows up as experimental nvidia...not sure what I should do. I would really like to use this card. Could it be it's not getting enough power?