You're correct, but if we're talkin about twitch streaming then you don't wanna go too much above that.
And I doubt anyone can see much past the 120hz screens but I could be wrong. I could have sworn I've read that we can't resolve much past 60fps...but just now read something contrary to that. So in that case I guess a drop from 150 to 90 would be noticible
those competitive fps players like to play at like 300fps. even if you can't 'see' all those frames, it's gonna make the game feel more responsive
because a 300 fps dip to 200 fps will still be smooth (and rarer on low settings since explosions etc take less of a fps hit and shadows are off etc) but a 90 fps dip to 45 fps dip will be very noticeable
I play on a 144 hz 1 ms screen average FPS around 140-160 on max settings on Overwatch
when they released the new patch this past week, it reset my settings to 60 FPS I thought my computer was dying

felt like I was playing in slow motion

started to panic until I realize my settings changed
changed back to 144 hz glory
the gap from 144 to 240 is very less noticable than from 60 to 144 though
edit: twitch streamers were doing 3 mbs and now they upped the limit to 6. 2 is way too low to stream at any good quality above 720/30 fps