Technically there is no definitive proof that overclocking your display decreases lifespan of the panel. Its also very common for manufactures to apply a "oc" to a standard 60hz to achieve 120hz/144hz, assuming you know the model#/manufacture date/and manufacture you can look up your panel to see the highest stable refresh rate. 

 Technically 2: you arent really "overclocking" rather you are forcing a "overdrive". Overclocking really only applies to things that have a clock value, but bc its the internet and most people are to lazy to point out the difference, its pretty known at this juncture as "overclocking"

 It should be stated though, overclocking can cause issues with color and gamut depending on panel type. (example: IPS displays will desaturate colors and washout blacks the higher you push them)
 It always pays to actually know what you are talking about before dispensing advice; a "oc" 60hz panel will run at the higher overclock above stock refresh rate and it can be verified either by using Testufo.com or dedicated panel performance hardware(just use testufo, most people arent going drop $1k on panel performance metrics for just an OC). 

 To those of you who believe you cant perceive a noticeable difference between say 60hz & 78hz, you are right in that the differences are miniscule but it can be seen provided you know what to look for. OC'ing you display has 1 added benefit assuming you find a stable clock, you can use v-sync at a higher refresh rate (assuming the game permits it, or doesnt have set standards in place). 

EDIT: here a very good article fer y'all to get edumacated: https://forums.blurbusters.com/viewtopic.php?t=4522