I haven't tried yet, but if you free the pc-monitor from its housing, the viewable area should be the same, as there most likely some picture get lost in the case.
Most classic arcade monitors are 19"
Yep, I really would consider to go with 19", for its the real thing!
A arcade-monitor (or an WellsGardner U3100) would look most perfect for arcade-games, but not for windows.