Add 120FPS cap to System Config menu.

[wicked-one]

Human eye can't make the difference between 60 FPS and 120, what would be the point ? (Genuine question)

from a bionic point of view, right... human eye´s and brains compability are limited to even lower rates. around 24 images per second, iirc.
still, you will notice a difference when looking at higher refreshed displays.

Graphic Card´s achieve really high FPS rates these days. My GTX970 boosts my Game to 120-180 fps at max. Details

You want to sync your Monitor refresh rate and fps, so you can avoid things like tearing. which, tbh isn´t quite recogniceable at 120/144 Hz displays.
The image get´s there refreshed so often that you barely are able to notice, because of reasons you mentioned. (at 60 Hz this could really rain on your parade)

Another advantage i just made up is ressource management. there is no point in rendering 150 fps in your GPU if your display only can output 120 images.
so your GPU calculates 30 fps which you will never see ... avoiding this by limiting to a specific rate saves you unnecessary cumputing which is > lesser tpd > lesser heat > lower coolant fan rate

which ultimatively results in "more ambience and lesser FROOOOOOOOOOOOOM"

i just realised how much i miss my gtx970 (getting rapaired atm) whilst my replacement is an Radeon HD48xx

Man i tell you, skipped all my cutscenes in Starcraft 2 because every dialouge was not understandable due to the noise of the Radeon´s fans