My own experience with dsl max was a bit disappointing in that BT guesstimated i'd get 6-8Mb but in reality I ended up with the line syncing at around 1.5Mb but because of the way they rounded down I had 1Mb.
Adam Have you tried to remove the house internal wiring. I live in a 12 year old house and it brings my speed down from 3.5m to 1m when I have all the internal wiring connected!!!! If you have a "split face plate master socket" then you can remove the bottom half and plug directly into the socket inside. This should remove all the internal wiring and have a "straight to bt" connection. Try and see what sync rate this has on your router. It will take a few days for the BRAS rate come up. Also on this detachable front plate you can remove the wire on connection 3 (or 4 ) as this is just the ringer circuit - you just need wire 2 and wire 5, usually white/blue and blue.
HTH Keith