I have a 6c stock nMP. I have been using iStat Menus and one of the displays is a bar graph showing memory usage of the graphics cards. When using Mavericks, card 1 memory shows not being used and card 2 memory shows small usage as that card drives the display. When running Yosemite, card 1 still shows not used, but card 2 shows steadily increasing memory usage over time fairly quickly ending up with about 90% usage where it stabilizes. This happens even if nothing is running other than the OS. When I run Handbrake on Mavericks I get about 95-99% CPU usage. When I run same compresses on Yosemite I get 85-90% CPU usage. Seems strange and I am suspecting it is because of what is happening with the graphics memory. Possibly a memory leak of some sort in Yosemite. I was wondering if anyone else is seeing this. I have returned to using Mavericks for now.