If you were using G wireless it would only do ~22Mbps so I guess you must be using N and you'll have at least a 100Mbps switch on the old ADSL kit so why you see the big speed drop connected to your old router is a bit of a mystery to me. Maybe somebody else will have some ideas.
You can change the base IP setup on the SuperHub to match your existing network but I've heard it can be a PITA because of issues with the guest network which defaults to 192.168.1.n
I just bit the bullet and reconfigured all my fixed-ip stuff to fall into the SuperHub default 192.168.0.n scheme.
If you use the "Reserve IP" option it reboots every time you add or remove one (plus on one occasion corrupted the entire table for me) so I just hard coded all my fixed IP stuff in the 120 range and set hub DHCP to start at 140
====
It occurs to me you may have just meant change your WiFi kit - you can set the Hub SSID and password in the advanced settings.
If you can't fix it with a hammer you've got an electrical problem.
Edited by kwikbreaks (Wed 20-Apr-11 12:38:45)