I've checked refresh rates in nvidia-settings app. And I found that settings without __ are useless.
I have these variables in xinitrc
But for example
__VDPAU_NVIDIA_SYNC_DISPLAY_DEVICE="DFP-0" vlc sintel-2048-surround.mp4
is not working for me.
Try modify your xinitrc (GDM use /etc/gdm/Xsession, KDM /usr/share/config/kdm/Xsession, SLIM $HOME/.xinitrc, without login manager startx use $HOME/.xinitrc).