Another trick is to remove the bell wire from your mastersocket.
Older BT phones used to have a bell wire for ringing (they would send volts down to activate the "hammer" inside the bell). This is not needed on new phones. From testing here there can be a lot of noise induced in the line down the bell wire even though it is not connected anywhere. Quite a few db's worth of noise too which has a massive effect on maximum speed (between about 1.5-4.5 mb).
BT sell a thing called an "Iplate" which is about a tenner. From my testing here though removing the bell wire has the same function as fitting an Iplate. Although in the "real world" you might not see as much of an increase as I mentioned above, well not all the time, maybe 1-1.5mb Techinically your not supposed to touch any of the wires behind the master socket..but meh who cares huh!