Just a quick query, Chrys, as I don't want to hijack this thread . . .
Regarding the NTE5/A that you removed. Was it a BT original from the 1980s, with three screw terminals (A, B & earth) plus a gas-discharge tube over-voltage protector?
I have a vague recollection of either Ezzer or Black Sheep mentioning that the gas-discharge tubes, when sufficiently aged, had been found to have a detrimental effect on an xDSL signal.
(Needless to say the NTE5/A, installed in The Cattery is a 1980s BT original. The gas-discharge tube glows a very pretty violet colour when ignited by 500V DC. Tucked away in my what-not is a brand-new NTE5/A, manufactured in 2013, that has yet to be fitted . . . )