I have been away and not kept up with your later posts, it is frustrating that your IP profile has increased significantly but something has happened to restrict your throughput to 20Mbps. PlusNet don't seem to helping much either, I would definitely refuse the engineer visit, I don't believe that anything could be done. I have seen a couple of reports recently, on the plusnet forum and tommy45 here where the BT Wholesale IP profile has suddenly changed to something like the previous expected levels. Something is going on in the background.
I certainly agree with you that if you are syncing at full speed you should get the best possible results from the service, not some restricted speed caused by incorrect calculations in the DLM system.
I have a hunch that may explain your low speed. The PlusNet rep who said that the BT wholesale IP profile or BRAS rate is no longer used is wrong. PlusNet use BT Wholesale backhaul so it uses the IP profile to control the throughput. I think the guy is confused and was mixing it up with PlusNet's own profile system known as "Current line speed" which tracks the BT profile (usually about 0.1 to 0.2Mbps below it).
This is the profile that is now not generally used by PlusNet because a few years ago they changed their network so that it was no longer required. It still exists but doesn't have any effect on speeds for most customers but not all. I don't know the detail of the change but the backhaul was moved to a dedicated BT Wholesale system.
Now for the interesting bit, if you have a static IP the connection is handled in a different way and the PlusNet current line speed is still functional and can restrict your speed.
You can check this by logging in to your member centre account and on the broadband tab there are some speeds listed, see what it says for current line speed.
My idea could be completely wrong but there have been cases where the current line speed for no particular reason changes to a default value of around 21Mbps which is the maximum ADSL2+ profile.
I wouldn't try telephone support to sort this, if it is the profile problem, they probably wouldn't understand.
I would suggest posting on the PlusNet forum, there are some staff on there with good technical knowledge who have a lot of experience and may be able to help. They have sorted out a few problems for me in the past, but generally I have had very good service.
