Having concluded my modem cable experiment...
Vince (mr..telephone) states that he will be reopening his ebay shop on Tuesday 29th Aug so it still might be worth getting a top quality CAT5 or CAT6 rj11 to rj45 lead from him.
I've got one of his CAT5 (solid core) rj11 to rj11 leads and at some point I may remove one of the rj11 plugs and hardwire one end to my Mk3 faceplate's A&B terminals. Hardwiring CAT6 to a Mk4 plate could be tricky though if you do restart your experiments
Edited by 4M2 (Fri 25-Aug-17 17:46:45)