Deniz Dogan
What *really* is bothering me though is that not even "emacs -Q" with a clean .Xdefaults works properly. Even then the width/height are off!
From this, I draw the conclusion that there is something fundamentally wrong in either XMonad or Emacs, and I'm kind of leaning towards believing it is the latter.
It's surely nothing to do with xmonad. However, emacs seems to work for other people, which suggests it's not emacs. (That's not to say there aren't problems with this aspect of emacs---there surely are.) The debian package (which I'm also using, though I'm building my own from more recent checkouts) mostly adds a few patches to better fit in with the debian elisp packages and a few other things. Nothing relevant to this, as far as I can see.