Unity is a Compiz plugin, and when Compiz cannot detect the refresh rate it defaults to 50hz.
This normaly happens on my Nvidia proprietary drivers.
Why the hell would they default to 50hz?
Who decided that 50hz would be a smart fallback?
Is Ubuntu’s main consumer PAL TV Stations?
But still, I have had this problem for quite a while now, and only last week I got angry and sat down to figure out what the heck was going on.
To fix this, you have to MANUALY go into ccsm and input the correct refresh rate EACH TIME, since it does not save upon logout/reboot.
Or just make a script and add it to startup programs:
sleep 5 &&
dconf write /org/compiz/profiles/UnityNeu/plugins/composite/refresh-rate "60"