Did BT really disconnect your ring wires? I didn't think they did that. If you really have no ring wires or an iPlate or one of the new BT master sockets that have a choke in the ring wire was fitted you will probably see no gain from a filtered faceplate other than they are a lot tidier.
The reason filtering at the master socket end of a plug in extension is preferable to at the equipment end is because plugin extensions carry a ring wire which will only be isolated from dumping it's picked up noise onto your ADSL signal by a filter, an iPlate, or one of the new BT master sockets.
You obviously can't filter a plugin extension at the master socket end if you want to run your router on it though as there would be no ADSL signal left.
Your best bet is to run the test already posted.
Edited by kwikbreaks (Wed 03-Aug-11 12:36:57)