On a recent project, I've been using masks around the faces of a couple of people I interviewed for a project (aka Power Window)

I couldn't for the life of me til this morning figure out why I couldn't get RT playback of the footage - I discovered if I deactivate the mask, RT playback happens, reactivate the mask, frame rate on the timeline at 1/2 preview mode barely allows for about 15-18 fps.

Are masks GPU accelerated at all in playback? I tried my old Radeon 6970 2GB card last night to test my theory and saw no difference in performance compared to my GTX-660ti (Yes old cards - not going to swap out any more hardware until I finish current projects for clients) - I'm in the process of researching which GPU to go with moving forward.