In reply to a post by NaNook:

Is that the new router they have brought out?

I am not sure if it is the latest but this is the one they started to send to customers when they complained about the poor performance of the HG633.

The 'new' router is a Sagemcom FAST5364, which is their latest 'best ever'. I had one sent last week because I took advantage of a fibre upgrade, but as I don't have experience of fibre with the HG633 I can't say if it's better.

The HG633 worked well for me on ADSL. 134 days of uptime after updating to v2.00 firmware with no resets or issues before I swapped it for the new one. Never got the D-Link router.

However, that's got nothing to do with answering your question but I hope you get a successful resolution.

As you've seen similar results with two different routers, the line stats clearly show your issue is the phone line itself, not throttling. Either a poor quality line or very long line between your house and the nearest street cabinet. Where and how do you have your router connected to the phone line - e.g. master socket, extension, which kind of microfilter, etc? And what type of master socket do you have? I have seen microfilter and in particular filter faceplates make a huge difference with fibre.

The line is around 2 miles long.

The oddity is when I connected the Netgear, the speed and stability shot up, then slowly decreased back to lower than I had with the TT router.

Router connected directly to one of those new master sockets that do not require filter, with all extension wiring disconnected.

Is your connection speed always listed as 18.00Mb even after a modem restart?

The high noise margin and rounded downstream figure suggests DLM has banded/capped your sync speed.
If that's the case it will never sync above 18Mb.

If talktalk are part of the DLM reset trial you could ask for 1.
If not it needs an OpenReach engineer to reset the DLM, or potentially months of waiting and hoping it removes itself (unlikely).