After researching all day, I've got some findings.
My current ancient CRT monitor provides roughly 14"x10" of screen, for comparison, at 1024x768 (768k pixels).
There are only three options that'll realistically fit inside the cabinet:
1600x1200, in a 20" monitor, is 17"x12.6". 1.920m pixels total. Fully 4:3. Also 16ms response time from grey to grey, so not great, and the only one available is $500.
1280x1024 is 5:4, and at 4:3 it's 1280x960. Only size actually available is is 19", or 14"x11" of usable screen. 1.228m pixels total.
1920x1080, in a 21.5" monitor, is 18.732"x10.537". The 4:3 space of that is 14.05"x10.537", with 1.555m pixels total.
So, surprisingly, a widescreen monitor provides about the same screen size as what I have right now, but with far more pixel depth. 5:4 doesn't actually offer enough improvement because it's only available in 19" form. 1600x1200 would be the best, offering the most pixels and the most space, but I don't think it's worth it for the amount of money it costs and the fact that it's not really designed for responsive graphics.
What do you think? Am I off here?