60 fps on 60 hz vs 75hz:
- from smoothness, no difference
- on 75hz, you have less chance of seeing screen tearing without freesync
remember! 75hz means also the max fps. If you have 75hz monitor and if you pc can push 75 fps, you will see 75 fps.
if your pc can do 75 fps but your monitor can only 60hz, you will see only 60 fps with high possibility of screen tearing, if you disable VSync.