I know, like how I moved to Plusnet and now only seem to be able to hit 60Mb when I was previously getting 75Mb with Zen you mean?
I was banded at 74 meg for months (it was triggered by me testing/trialing a Draytek Vigor 130) and it only got removed when I moved from BT to Plusnet 18 months back. It has been syncing at a solid 79999/19999 ever since.
I plan to move to Zen next month so it will be interesting to see how my line copes, especially because a few additional houses on my street have switched to VDSL2
I should be back here moaning about it soon