The human eye cannot see any fps above 60 so any frames above that are a waste of CPU power. If your monitor cannot display a refresh rate equal or higher that your fps then the additional frames are being discarded, hence the likelihood of rubber bullet syndrome. vsync clamps your fps to your monitors refresh rate to prevent frames being discarded.
For best results,
1. set refresh rate higher that 60 if you can. 72 if probably the best.
2. enable vsync
3 set max fps to 60.
FYI: most movies are displayed at 40 fps.