Taken from
http://www.freedom2support.net/
Dear all,
Today's the day that the first of a large bulk of MAX regrades have gone through. I've received a number of queries already, but please bear this in mind if you're experiencing slow downs:
First and foremost, I need not remind most people, but MAX is also a contended service. While you can still experience fast speeds during peak hours, you're more likely to get faster speeds during off-peak times (1am-6am).
Now, the fun part ...
There are two speeds involved, the sync speed, and a speed that's set in BT's BRAS.
With the latter, there's a known issue which means the speed in the BRAS doesn't get changed. BT are working on fixing this, but for most people this won't be a problem, especially after a few days at MAX speeds (more details here).
The first thing that happens when a MAX regrade goes through is it sets about determining your highest possible speed. Now in order to do this, it has to keep cranking up the speed to see what happens. Every telephone line is different and will respond differently. Think of it as a sort of stress test; in order to work out what the maximum possible speed is, it has to go a little nuts to find out what your line's limit is.
This whole process can take up to 10 days. During this time you'll find your line goes down briefly and then comes back up at a new sync speed. This is perfectly normal.
While your line's maximum speed is being worked out, it will likely be run at speeds that it can only support with little or no reliability. This can actually result in slowdowns, because as with anything, when it's working outside of its limits, it gets a little flustered and can't do things properly. Those with routers may then notice more errors in their logs, as well as their noise margin (AKA "signal to noise ratio" or "SNR") dropping through the floor. These can all add up and result in slower throughput, because while your line rate may be faster, it's ultimately lost efficiency.
So please give your regrade some time and let the dust settle.