[t2ffn]

I'm not sure what you mean re: overscan. You can't set your content to a fixed refresh rate, as some stuff would play strangely, surely?!

I'm trying to say set it such that:

Settings > System > Display > Monitor > Refresh Rate = 50Hz (or whatever Hz your TV doesn't think is a PC)
Settings > Player > Videos > Adjust display refresh rate = On start / stop

Then you get a set refresh rate on the menu and when you press play, whatever video you play, Kodi changes to that refresh rate so the video playback is smooth and at the right refresh rate.