Out of curiosity, can you provide system profiles for one or both of Macs, using /Applications/Utilities/System Information.app? That gives us more details to work with.
Also, can you try seeing what framerate is in editor for 4.4? From main menu bar > Unreal Engine > Preferences… > General > Miscellaneous > Performance > Show FPS
It seems a bit odd that 10.10 beta is causing animation to fall over in 4.4 and not 4.3. I’m not aware of any changes we made that could explain that at all.