After replacing my BT supplied Huawei HG612 FTTC modem and Home Hub 3 (or latterly 2920n) with a nice new 2850n and- despite much messing with firmwares and configuration options- I became disappointed with the speeds obtained. BT reset my profile twice- and it still reverted back to a download speed 20mb slower than the BT equipment. The upload was also 40% slower.
So, after some more investigation online- I found that some people were having issues with the matching of the modem chipset to that in the DSLAM cabinet. According to the Draytek- my cabinet contains an Infineon (Lantiq) chipset. My Huawei HG612 has a Broadcom chipset- the Draytek has a relatively unknown chipset by Metanoia Comms. The alternative BT modem, made by ECI- has a Lantiq chipset. So- by way of an experiment, I have bought one on EB@y. It should be here this week. In the meantime, I have put back my original Huawei modem and the Draytek 2920n. Already, my upload has gone from 9-11 to 16, and hopefully DLM will allow the download to increase over time. It will be interesting to see if the ECI modem gives further improvements or not. Has anyone else seen anything similar with their setups?

Sorry replying to your thread just want to add something
At least mine has ADI and not metania unless metania using chipests from ADI
With adsl, ADI and infineon (at TT LLU)is working and synchronise very good so i am surprised you having issues (i know you have vdsl line)

Now there's a thing!
After my third complaint- a very nice lady at the BT India call centre arranged for an engineers visit last Friday. The engineer from Openreach turned up just after 1pm and finished three hours later.
It turns out there was a copper line fault between my house and the DSLAM which was introducing errors and causing the DLM to cut my speed. He has corrected the fault, reset my IP profile and all is as it was when it was first installed last year. So, all I need to do is to retest the 2850n on my newly fixed line and see if it performs as it should. Happy days.... I think!

Did your line perform as it should now with the 2850n?

Sorry it's taken me so long- but I have finally reconnected my 2850n and loaded on the latest 3.6.3 HTC beta firmware (with IPV6 enabled so I don't get the server error).
I am pleased to report that speedtest.net is showing 71mb/s down and around 13mb/s up. Slightly slower than the Huawei for the upload- but who cares
Just need to load the config settings from my 2920n and then I shall leave it for longer testing. But it's looking good now with very low FEC errors.

The 2850n is now permanently installed and performing well. Syncing at 75mb and 20mb up.
An interesting observation tonight though- my snr has not changed once it has gotten dark. Normally the snr would rise and the sync speed could drop slightly- something that used to affect my adsl line quite badly. However- tonight it has not changed at all. I'm wondering if it has something to do with the recent replacement of all the local street lighting with new led lamps- replacing the old sodium fittings. Could it be there is less radiated noise? If so then it is a big bonus!
UPDATE: 3 days now and the snr has not changed. Connection rock solid. My internet has never- going back to the days of dial up modems- been this stable.