The FECs dont affect your speedss.. but the CRCs do and I'm not too happy about those.
For your uptime (if ive done my maths right 13,200 seconds), then the CRC error rate is very high at more than 1 per second. Each of those packets will have had to be re-requested, which is going to slow you down even more... and anything thats time sensitve such as VoIP or streaming video is going to be bad
Routerstats is an excellent tool that we often use and has helped many track down the source of interference... however if you are on a 3dB profile, its not going to give the line much leaway.
There's "something special" about the 3dB profile in that its very seldom used.. and only on the longest of lines in order that some sort of sync may be attained and usually reserved for the very slowest speeds. I suspect that if and when your line drops, the DLM will possibly bump you back up to 6 dB then in a few days or so 9dB.. and your line will be more stable, but your actual sync (connection) speeds will be bad. Then when your sync speeds get too bad.. the DLM will drop you back to 3dB so you can at least get a connection.
I have a horrible feeling that this is an event that could go round in circles of up and down speeds.
There possibly is some interference somewhere that may be adding to the noise.. and thats what we are hoping will show up. Because your line is so long then its more subsceptable to noise.
Pardon the pun but theres 3 lines of thought. - Either the twisted pair youre on from BT isnt as good as your neighbours, or you are picking up some interference not picked up by your neighbours... or for some reason your line just cant cope with maxdsl and you may be better on a fixed rat 512kbps line. The final option would give you a much more stable line, you'd have no profiles to worry about - no ups and downs - and hopefully not as many errors as youre seeing now. It would be slower, but it would be more consistant.
We can have a go with routerstats if you like and see if it can pick anything up.
Out of interest your neighbour who gets 2Mb - which router do they use and do you know what their attenuation is?