We did some testing with 165hz, and 240hz monitors, (Esports studio) we found that almost everybody could tell the difference between 60fps and 120fps - the difference is night and day, however once you get above 165hz into 240hz - it becomes a lot less apparent, I don't remember anyone reliably being able to tell the difference between 165 and 240, any better than chance.
Back in the day, late nineties / early 2000s I used to play a lot of competitive QW, and later into Q3 - A number of us (from what I can remember) bought Iiyma vision master CRTs, which would do 200hz refresh at 800x600 (from memory), and the difference was literally mind blowing, to go from 60hz to 200hz on a CRT - it was like going into a new world.