Our 2010 2.93GHz 12-core MacPro with GTX 980ti couldn't edit complex 4K footage smoothly in Premiere Pro CC (in OSX El Capitan or Win10x64Pro). FCP X for the most part can handle medium complexity 4K (chroma key, multiple 4K streams at once, very high resolution stills (Ken Burns etc.). However, I'm quite a bit faster in PP CC, and I need to research plugins to replicate what I can do with Lumetri (if such a plugin exists). It was time to upgrade the video editing machine, and it seemed like bui