Unfortunately, the biggest source of interference is going to come from neighbours getting FTTC too - and so could come at any time, before or after you connect yourself. The impact would be seen by DLM intervention that steals 10-20% of the capacity of the line, which (I think) is what was happening on my original line.
Just one comment to add:-
For connections unable to max out a 40Mb/2Mb service, increasing the US profile from 2Mb to 10Mb can increase US speed, at the expense of some DS speed.
I conducted extensive tests & experiments in conjunction with my ISP, Plusnet using differing connection profiles & on my own connection when US profile is 2Mb, I can achieve around 32Mb+ DS sync speed.
When using the 10Mb US profile, I can achieve around 5Mb to 6Mb US sync speed (i.e. 3Mb to 4Mb increase) at the expense of DS sync speed reducing to 28Mb to 29Mb (i.e. 3Mb to 4Mb decrease).
e.g. currently in sync at 29262 kbps / 5782 kbps, against attainable rates of 35100 kbps / 5804 kbps.
Last week it was 28543 kbps / 5582 kbps against attainable rates of 33356 kbps / 5687 kbps.
Maybe coincidence, but I ALWAYS seem to achieve slightly higher speeds when the weather is wet & very cold.
This week, temperatures have been around -5 degrees C earlier in the week & it has been very, very wet for the last couple of days.
My D-side connection is anywhere between 850m & 1000m from the PCP (depending on the exact, unconfirmed route), with the fibre cabinet itself being around 30m or so further away.
The connection resynced "on the fly" at its currently higher speed yesterday morning.
Whenever DLM has been reset following many external fault repairs, at a wide open profile, (interleaving completely OFF), DS sync speed has been as high as 36Mb until DLM takes action to improve stability - usually within the first couple of days, but very occasionally around 8 days or so later.
As I monitor my own connection (& some other users' connections) somewhat obsessively, I can state that all my comments are based on empirical & factual data.
P.S. My connection doesn't seem to be affected by Christmas lights - not too many houses on the way from the cabinets (in my direction), but our own aren't on (yet).
I have, however, seen some other connections suffer (slightly) due to Christmas lights being switched on.
Edited by Bald_Eagle1 (Sat 15-Dec-12 08:55:24)