Hi!
Yosemite Beta user here but unfortunately DOS runs much worse on it compared to Mavericks. Maybe it's because it takes up an extra Desktop instead of going full screen on the primary Desktop space. I know this is also the case on Mavericks, but maybe Yosemite tries to force the blur effect somehow.
Either way, medium runs maybe at 10-15 FPS now. My system info:
http://glui.me/?i=vs9xcq1103ge45r/2014-07-26_at_13.53.png/
