First time fibre install on possibly faulty line?

I'm thinking of having fibre installed (I currently have standard ADSL).

The checker says I should be able to get 71Mb-80Mb downloads, and I can see the green box from my window - so in that respect everything should be fine.

However, I think there might be a fault on the line. Sky Broadband connection statistics are (this is my backup connection, and the one I use everyday is fine):

Broadband Link Downstream Upstream
Connection Speed 381 kbps 413 kbps
Line Attenuation 60.5 dB 36.1 dB
Noise Margin 18.7 dB 15.9 dB

I've changed the microfilter, with no improvement, and done the quiet line test where I couldn't hear anything out of the ordinary.

So my question is how do you think I should approach the install?

Should I try to get any problem resolved first, and wait to see an improvement in my Sky Broadband connection, before ordering fibre?

Or should I just go ahead and order fibre?

Order fibre. There's a good chance that if you have a line fault, it will be between the cabinet and the exchange rather than the cabinet and your master socket. Also, if your fibre connection fails to meet the estimate, it will be repaired free of charge.

Low speeds on Sky ADSL2+ LLU for longer lines is often down to their cautious DLM system rather than a fault.

You will be dropping some 5km of copper to only be using 100m or so once you switch to FTTC.

Thanks guys, I'll go ahead with the install.

At the moment, I have a pretty much unusable backup connection so have nothing to lose.

My main concern was that I might find myself "stuck" on a low fibre speed if I had it installed it on a faulty line, but that was just uneducated speculation on my part

Other than the exchange being 5 or 6km of copper cable away nothing to suggest a particular problem

The high noise margin may indicate a problem

A line test is performed when you order.

If a fault is found an Openreach engineer will be required. You won't be sent a contractor and a self-install won't be offered to you. The Openreach engineer then gets sent to you to do an FTTC install plus "fix line fault" and they are told what the fault is.

If you are offered a self install or if a subcontractor shows up, the system hasn't detected a fault.

That was my thought. There's probably quite a lot of noise pickup, and with that level of attenuation if the domestic wiring isn't optimal then it could suffer quite badly. However, if the green cabinet is that close even that might not matter.