This is one of those things I always thought of but never got a chance to fix. I found it a bit irratating that my display was always being detected at 50 Hz. I thought that this was a bug and just waited and waited for updates, but in the last year it’s still there. First thought that this may be a Gnome bug but when I got to KDE, it was there too. Took me awhile to find out, but fixing it is easy enough.
For a single monitor screen, the nvidia driver will set an incorrect display rate for the xorg server by default. This is because the nvidia driver by default enables DynamicTwinView (dual monitor support) and if an option isn’t set to disable it, will not detect the refresh rate and will automatically set a compatible rate of 50 Hz. nvidia considers this a useful feature for people with dual monitors for automatic configuration, I however think it ignores most of how the Linux nvidia users use their computer. Hopefully though, nvidia will get past this and fix it sometime soon. Until then, to disable TwinView put in your ‘/etc/X11/xorg.conf’ devices section:
Section "Device" Identifier "Device0" Driver "nvidia" Option "TwinView" "0" Option "DynamicTwinView" "0" EndSection