Well here is a dumeter snapshot of me doing some experiments.
speed left of graph is ftp on high port right of graph is http
Left of graph is download of a ftp on a high port, and the right of graph is a download of the same server from http done at around 9pm, this is on 2mbit.
After mega tweaking and setting rwin ridicously high at over 250000 can get it stable at 220kB/sec and after 1am this increased to 240kB/sec.
Speedtests from robin walker site wont be fair representation of ntl's external capacity performance.