if you go for the above mentioned face plate then this should take your internal wiring out of the equation in relation to performance issues on your broadband.
It dosn;t matter wether it's old wiring or brand new, it's an antennea which can potentialy pick up some interference which broadband may overhear. The bell wire is usually the first culpit on it's own, but by no means the overwhelming one, the other 2 wires can do the same (hence the face plate)
Openreach broadband engineers can carry data extention kits which come in 5,10,30m lenghts (sounds a lot but a properly fitted cable over door frames, round skirting boards eats this up) one end plugs into the dsl output, the other end has a dedicated socket for broadband) in case the master socket with the full face plate is not where the modem/router needs to be sited. Although fitting this WILL cost you.
Otherwise you can get longer cables to run from either from a microfilter or the filtered face plate from any computer wear shop, belkin do some nice ones with a strong outer sheath. although the longer the cable the better emf reception as an antennea, Will it put you back to square one, perhaps it will, unfortunately only one way to find out. to try it practicaly