Yeah, if you're lucky enough to have a U5000 monitor, it's standard/medium switchable. Sucks to not be able to use it's max resolutions, but at least it would be usable.
On another note, why CAN'T we use meduium res monitors for Mame? No one has written a driver to get our vid cards to that rate? I figured it'd be easier to do 25KHz than 15KHz, but what do I know.