I don't know if this is the same problem - but last night I tried to
use xemacs-21.0b61 via telnet over a slow modem (I got 33k). It was
awful. Trying to display things in the shell mode was drawing about 1
line per second.
Quitting emacs and just using a bash shell, performance was much much
better. Not good, but much much better. I don't know if this was a
difference in recent xemacs, or if I just got a particularly bad
connection. To try and diagnose, I fired up POEMACS (plain old fsf
emacs). It wasn't great either - and I'm not really sure if it was
noticeably better.