Just as a quick, alternative suggestion...
I have an actual arcade machine that i use as a mame box... with the old monitor and everything... there's a lot that can go wrong with them with age... and they have to warm up and stuff. I know you'll be getting a new one, but...
You said it was a big purchase for you. For this reason, I would lean towards the high res monitor, because if anything goes wrong, you'll have a piece of hardware with re-applicability... or... if you find that you aren't playing your arcade machine as much as you had thought, you can pop the monitor out and re-task it for another project (like a media-box or a home automation machine, a dumb terminal, or any other various tasks that would be more fitting of a high res monitor instead of an arcade screen)
The high res monitor will satisfy all but the most discriminating of players on your machine, and while some ancient arcade enthusiast such as myself might be able to tell the difference between properly interlaced and resolution graphics in all the various versions of pac-man and street fighter, for the purpose of gameplay, it is all essentially irrelevant. The monitor will suffice, you'll have a lot more vendors and form factors to choose from, and you might even end up saving money.
Anyway, good luck either way that you go. If I had it to do over, my machine would have a high res monitor in it. (I don't really care about the "proper" resolutions... (I find it funny that some people really do... and they get all uptight about which control scheme you use for "arcade authenticity"... like which steering wheel? Well, there are virtually no two driving setups alike! So I say use whatever you like, from a wii-mote to a homemade wheel!)