Most older consoles has an aspect ratio slightly narrower than 4:3. E.g. PS1 is 1.219 (if viewing a game that utilizes the full visible space, with no overscan). This would then be cropped by the overscan of the CRT.
If it’s different between x3, x4 & x5 (in 1600×1200), then it’s something with the scaling on your display. Edit: ignore, forgot that x5 uses different base for sampling rate