Confusion

[#1]

Not enough difference to worry about.
When you say the extension cable was cut, are the remnants still attached to the master socket?

[#2]

Nah Jelv, the line is completely disconnected, has been for a few years.
Stats tonight might be healthier though?
Line Attenuation 30.5 db 13.0 db
Noise Margin 10.35 db 33.5 db
I'm not sure how low that noise margin should be.

[#3]

The background noise increases at night which leads to a lower noise margin. What we like to see is the noise margin stay above 6. If you reboot tomorrow between 10 am and 2pm when the noise margin is nice and high you should see it sync at a higher speed. That will give you the best speed your line is capable of supporting. The noise margin immediately after the resync will be the target BT have currently set for your line. Keep an eye on the noise margin from there on to see that is doesn't drop too low.

[#4]

Will do. Thanks mate.