NVIDIA X Server Settings lost on every reboot

1. Create a xorg.conf file by:

   sudo nvidia-xconfig
   

2. Look for the Section "Device" part in the xorg.conf file And add this line inside the section:

   Option "RegistryDwords" "PowerMizerEnable=0x1; PerfLevelSrc=0x3322"
   

Save and reboot your machine.

PS. If you add more parameters, add ; after 0x3322

From the official user guide:

"4. Loading Settings Automatically

The NVIDIA X driver does not preserve values set with nvidia-settings
between runs of the X server (or even between logging in and logging
out of X, with xdm, gdm, or kdm).  This is intentional, because
different users may have different preferences, thus these settings
are stored on a per user basis in a configuration file stored in
the user's home directory.

The configuration file is named "~/.nvidia-settings-rc".  You can
specify a different configuration file name with the "--config"
commandline option.

After you have run nvidia-settings once and have generated a
configuration file, you can then run:

    nvidia-settings --load-config-only

at any time in the future to upload these settings to the X
server again.  For example, you might place the above command in
your ~/.xinitrc file so that your settings are applied automatically
when you log in to X.

Your .xinitrc file, which controls what X applications should
be started when you log into X (or startx), might look something
like this:

    nvidia-settings --load-config-only &
    xterm &
    evilwm

or:

    nvidia-settings --load-config-only &
    gnome-session

If you do not already have an ~/.xinitrc file, then chances are that
xinit is using a system-wide xinitrc file.  This system wide file
is typically here:

    /etc/X11/xinit/xinitrc

To use it, but also have nvidia-settings upload your settings,
you could create an ~/.xinitrc with the contents:

    nvidia-settings --load-config-only &
    . /etc/X11/xinit/xinitrc

System administrators may choose to place the nvidia-settings load
command directly in the system xinitrc script.

Please see the xinit(1) manpage for further details of configuring
your ~/.xinitrc file.

"

On Linux Mint 18 Cinnamon go to the little config app named monitors. When pressing "apply" a file ~/.config/monitors.xml is saved which serves the same purpose than the xfce displays.xml - it saves all those settings, that in nvidia settings are not persistent. You have to play around to change something (to trigger the availability of the apply button) if you happen to have configured your display layout in NVIDIA graphic settings panel. I did this AND added the load-settings from above to xinitrc.

I wil check if my window-reordering problem after the screen lock was active is gone now All windows reordered to main monitor