Not entirely what you want, but you could use my 'ArcadeVGA MAME Resolution Tool' (from my download page, click www on left).
This lists ALL the native resolutions used by the games in MAME. Standard res games will have up to 288 lines (a little more in some cases) in one dimension, so anything above that cannot be displayed 100% accurately on a standard res monitor. I believe VGA (high-res) begins at 640x480, so anything that or above will not display 100% accurately on a standard, or medium res monitor.
The ArcadeVGA has numerous modes to cover all standard res games. I have no experience with medium res monitors, but I believe the ideal solution is the WG 9200 + ArcadeVGA, as this monitor can handle medium/high res modes too. I think Hantarex make a similar model, called the Polo Star or similar...