WOW!
That's the first time someone has quoted me..

There are 2 great resolution to play MAME on a real monitor and ArcadeVGA card along with MAMEWAH.
- 640x480
- 368x240
The first allows you to see more details and stuff on the screen, but the screen won't look that good because it will be interlaced.
The second one will show less detail but will be crystal clear like any game since it will not be interlaced.
So run windows @ 640x480, MAMEWAH @ 368x240. Any vertical games and all midway games (mortal kombat, NBA JAM, etc) run at 640x480 with H/W stretching on. They'll flicker, but at least all the details would be there. Otherwise, you'll be missing a lot of lines from the top & bottom! (if your screen doesn't roll back on you!)