If you are using solid core 100% copper cat5e cable for the "data extension" you may find it better to hard wire from the A&B terminals on the Mk3 plate to a dedicated rj11 socket in your "comm's room". A rj11 plug on the modem/router end of the cable would also be OK but generally speaking a flexible stranded DSL cable from a dedicated rj11 socket to the modem/router could be more suitable depending upon the situation.
I have indeed used solid core 100% copper cat5e cable and the A&B terminals from the Mk3 Face plate.
At the moment its just terminated in an RJ45 as that's what my Modem (Fritz! Box7360 V2) uses for the wan port.
I like the idea of an RJ11 socket though as its more future compatible, ill have a look for one.
Various (Dile up) -> clara.net (Dile up) -> TELE2 (Microwave) -> ZeN (ADSL) -> ZeN (vDSL)