My last info was a little incorrect. My /etc/ppp/options file reads:

mtu 576 mru 512 lock

Since the MRU needs to be less than the MTU. (essentially MTU- header size). Actually, I have noticed that I connect quicker as well as view pages quicker.

If you remember seeing those dreadful adverts for windoze users saying "speed up your modem", this is essentially what those programs do. They also usually nag you with popups as well, though!

Ricardo