FTTC and Line Speed

[#1]

Hi All,
I have been with plusnet since the Force9 dialup days and always been happy with the service.
I final moved into area with had FTTC.  The house I moved into did not even did not have a master socket. BT Open reach Enignner came out installed one,
I just wanted to clarify a couple of thing.  As you cant see the sync on the router now as the BT modem does this for you and i have no login details. I can see that you can login to the plusnet portal to see this. It show you your current line speed is this correct?
According to BT i should get 66Mb.
When i first had it installed FTTC it reported 81mb
When i ran a speed test i was only get 6Mbps down and 10Mbps, Spoke to Plus.net and my profile was still on ADSL. Plus.net change this and got me turn the BT modem and router for 10 mins. When i powered it back on i was syncing at 42Mb and now get download speeds at 40Mbps and uploads of 8Mbs. Spoke to Plus.net who are currently looking to see if this is a issue with line.
I just want to understand with the sync speed is it like ADSL depending how far way from the cabinet/exchange and the quality of the line determine the line speed?
Can plus.net /BT force the sync speed / set limt on the sync. As it seem odd my first sync speed was 81Mbps and not only get 42Mbs.
If any one got the any guides on this it would be great.
Thanks for your help adn sorry if it been asked before
Al

[#2]

Hi and welcome to the Community Forums
Basically the way that Sync Works on FTTC is the Openreach Modem that is installed by an engineer makes the initial connection to your FTTC Cabinet. If you only live 100 yards away from the FTTC Cabinet, you can safely assume that you're likely to sync at a full 80/20.
The sync rate isn't capped as such, only to the point that it can't sync any higher than 80/20 on an 80/20 product. If you usually sync at 80/20 and that's dropped to 42/10 then it's likely there is a fault with the service that we need to look at. The point of failure is likely to be between the FTTC Cabinet and the Openreach Modem (in most cases).
One of the big things at the moment is Crosstalk. VDSL (FTTC in this case ) uses a higher frequency which does make it more susceptible to Noise/Interference/Crosstalk.
If your speeds have plummeted as you say they have, our Faults Team will take a look into it for you and will take this up with our suppliers.