I get the best PM performance using unity 5. But I can't publish a game to Steam w/out Steamworks, which requires me to upgrade Unity. It has partly to do with the amount of variables I have in the project, and how many FSMs I have in the scene. But even a lean scene causes a little delay.
I tried upgrading to a newer PM but it was worse. I just got a brand new machine, it didn't make a difference. However I wasn't expecting it to. When the long pauses happen, I don't get a cpu performance draw.
The pauses only happen when I select variables, or select the actions list. If I close PM editor, it takes just as long every time I select variables tab, upon reopening editor window.