Theoretically under ~24fps or ~25fps the illusion of correct motion doesn't work anymore. I see a pure slideshow at 20fps (on a 60hz screen) and a relatively smooth animated motion at 25fps (PAL stuff on a 50hz TV obviously), but that's me.
Would be interesting to test the exact threshold, in my case, when I'll get my hands on a gsync or freesync monitor.
Won't do you any good as they don't work under 30 I think.