100Hz vs 120Hz

[jtsoi]

How noticeable is the difference between a 100hz and a 120 Hz monitor in gaming? I was thinking of purchasing an Acer Predator Gaming X34 Pbmiphzx and since it stated it was overclockable to 120Hz but if the off chance the overclock fails horrible and miserably and I have to play at the base of 100Hz will I notice much of a difference between the 20Hz?  https://www.amazon.com/Acer-X34-Pbmiphzx-UltraWide-Technology/dp/B079FV8S5M/ref=sr_1_3?s=electronics&ie=UTF8&qid=1534348144&sr=1-3&keywords=Acer+Predator+34&dpID=41lx6KnkDtL&preST=_SX300_QL70_&dpSrc=srch

[WereCat]

Minimal but noticeable if you have a good perception 

[Cookybiscuit]

Nice to have but not enough to lose sleep over if you don't get it.