In pretty much all modern linux distros (including Debian), your screen's configuration can be found in /etc/X11/xorg.conf. In this file, there will be a line that says "Section "Monitor"". Anything in this section controls your monitor's behavior, including its horizontal and vertical refresh settings. You should be able to modify your vertical refresh rates (at the line that starts with "VertRefresh") so that there are 80 refreshes per second instead of the default 60. You will need to be root to do this.
If you choose the "Advanced" option in the installation, you can do this during the installation instead of modifying it afterwards.