I have a 60Hz monitor at the moment and I'm thinking about getting a 144Hz monitor but I don't know how much difference it usually makes - I usually play with vsync on in most games because with vsync on the game just feels smoother..... If I got a 144Hz monitor and wanted to use vsync this would mean that I'd have to make sure my games run at 144Hz and games like GTA won't run at that
So on 144Hz monitor with vsync off running at 80-100+FPS would the games feel smoother than a 60Hz monitor with vsync on
Let me try to explain
Vsync with 60Hz screen means that you'll get screen updates either every 16.6ms, 33.3ms, 50ms, 66.6ms etc. (equivalent of 60, 30, 20, 15FPS).
With 144Hz screen you can get refreshes at 6.9ms, 13.9ms, 20.8ms, 27.8ms, 34.7ms. etc (equivalent to 144, 72, 48, 36, 28.8 FPS)
So as you can see, you'll have much more opportunities for the refreshes. This basically means that when your FPS fluctuates, the difference between refresh times on screen fluctuates less on 144Hz screen than on a 60Hz screen.
However, if you GPU can handle constant 61-71FPS in a game, running it with VSYNC caps it to 60FPS/60Hz smooth playback. On 144Hz screen you'll be effectively capped to 48FPS speed, because it can't keep up with the 72FPS requirement that is needed for the next higher refresh. This would still be quite smooth, but obviously less smooth than on 60Hz screen. So the apparent smoothness would suffer from changing the monitor.
If you mostly stay under 60FPS with vsync on, then 144Hz screen provides better experience by having the equivalent of 48 and 28.8, 24 and 20.6FPS refreshes available, where 60Hz screen only has 30FPS, 20FPS and 15FPS refreshes available.
Also remember that nothing prevents you from running your 144Hz screen at 120Hz in case you are a lot between 72-60FPS figures. Then you'd effectively run similarly than 60HZ vsynced display with added smoothness in whenever you dip bellow 60FPS.
And there is always the option of tuning down few detail-settings to get contant 72+ FPS instead of changing your monitor to 120Hz setting.
How about g-synced display? Or even freesync? Though I'm not sure about the availability of those.
TL;DR: If your machine can keep FPS above 72FPS mark all the time, then you'll have smoother experience on 144Hz screen, because you'll be effectively running Vsync @ 72FPS / Hz. However, if you hover between 71-60FPS rating then 60Hz screen with vsync is better.
.....going from 60hz to 120hz/144hz is incredible. Add Freesync to that and you have the smoothest experience with zero tear and minimum latency as no need for vsync at all. I'd never ever go back to anything else now I've seen what a high hz panel with freesync/gsync does to gaming.