Keven, I am not using X via my modem, here.  I'm using it via ethernet
between two local machines.  It just happens that the machine that I was
running the X clients on was also my PPP gateway to the Internet.  When
using ssh to forward the X connection between the two machines, the
gateway was duplicating(?) data out the PPP interface.  (Maybe it was
sending something else---but it was sending _something_ out the modem in
lockstep with the X protocol packets going to my X server.)

The effect was that X clients (even xterm, etc.) were slow to launch and
very sluggish on interactivity.  And, any heavy modem use would slow down
whatever traffic X/ssh was sending out the modem, resulting in painfully
unusable interaction.

(I _have_ made actual use of X over ssh-protected dialup lines to the
Internet.  The performance was very comparable to what I was getting here,
evren though the only place I wanted data sent was over the 100Mbs
ethernet.)


  "I probably don't know what I'm talking about." --rauch@eecs.ukans.edu