vim. You can map font sizes and window sizes to keyboard shortcuts.That's interesting, i was just now looking for something like that for vim. Unfortunatelly, couldn't find any plugin for it.
yes, you can do things like:
set guifont=Lucida\ Console:11
where 11 is font size.
map <F5> : call Smallfonts()<CR>
I can code with fonts that small, because I like to get as much text as possible. Actually, an editor that had a two page view (or multicolumn) would be great, I kind of fake that with two windows editing the same buffer.