I did the same research than you ,I guess.
I could not locate any speedtouch Pro, with the four ports. Looks like there are not too many .
Found a lot of links to sites that teach you how to transform a Home version to a Pro version by changing some parameters on it.
I guess it is worth a try.
About the Linksys. That is the same model that I have right here on my desk. On my case it is working on cable modem, using dhcp, but i just opened the menu up and it does have the PPOe option on it.
The only trouble that i ever had with it , it was with the DMZ zone.
When I tried to put a Aplio Pro phone on the DMZ zoen, it did not work.
But when I port forward the right ports, It works like a champ.
Seems like the DMZ zone did not work, but it is a isolated incident, with a very particular piece of equipment (Aplio Pro).
Good luck,and if you need to run a test to another Quintum Gateway, let me know.
Write to mike3799@yahoo.com