After convincing them that it had nothing to do with my modem (since it affects at least one other customer of theirs, and my modem delivers full speed anyway),
And ruling out the foreign server as the problem before they even tried that one on (since other people get faster speeds on a single connection no problem),
And, of course, telling them I was talking about my download speed, not the upload speed, all relayed from me to 2nd level support via the 1st level dude because the 2nd level support staff "don't talk to customers" because "they just don't", in spite of the fact that it would be quicker, and less would be lost in the translation.
They wanted a traceroute. So I've sent one. So far, I've got the bog standard "do you want help setting up your PS3", etc email, and one largely canned response saying they'll look into the issue, and will get back to me "after further investigation".
Just for kicks, if you send their help desk automaton a tracepath and a traceroute, here is what it suggests:
Title: User Guide - Featurelink
Title: How to setup Playstation 2
Title: Set up a new Paradise dial up connection under Macintosh OS 8
Title: Setting Up PS3 with Broadband
Title: How to set up Nintendo Wii connection