Frequent disconnections - are they really necessary?

[#1]

Why does my PlusNet BBYW option 3 connection still get disconnected up to ten times per day ever since I applied for my free "up to 8Mb" broadband upgrade back on 14th August?  Is my connection still being regularly tested to see if it can cope with higher speeds?  If so can we stop it? I didn't mind being disconnected a few times each day for the first 10 days, while my line was being monitored, but it is beginning to get a bit irritating now.  It may have been a 10 day learning curve - but it doesn't seem to be learning much.
My profile is usually set at 5000 Kbps (sometimes 4500 Kbps and sometimes 5500 Kbps) and when connected with a downstream line rate of about 6048-6528 Kbps or lower I am quite happy. The system is generally stable and I get good download speeds of around 4700 Kbps (according to http://www.mybroadbandspeed.co.uk/)
Unfortunately, every morning when I power up, the Downstream Line Rate (according to my BT  Voyager 2100 configuration manager) is usually set too high again - something like 7648 Kbps or 7776 Kbps.  After a few hours, my line will be disconnected and it will then reconnect at a slightly lower downstream line rate (eg. 7584). Then a while later it will get disconnected again and after a few attempts like this, it will usually settle for the day at something between 6048 Kbps and 6528 Kbps - where things are generally stable.
Trouble is, the next morning when I power everything up again, the whole process starts all over again, and I get a downstream line rate of 7648 Kbps or 7776 Kbps again and surprise surprise after an hour or two I get disconnected again, until we get back to 6048 Kbps or 6528 Kbps again.
Why doesn't it just accept that 7648 Kbps or 7776 Kbps is too fast for my line and just agree to settle on something around 6048 Kbps or 6528 Kbps?  I think I would prefer to have a lower speed but not be disconnected so often.

[#2]

The behaviour you describe is quite normal - indeed one could say it is how maxADSL is meant to work.  The simplest way to stop it happening is to leave your router on 24 hours per day.  Then it will stay synced in the 6048-6528 range without any dropouts.
It is possible to manually adjust the target noise margin on some routers by tweaking internal settings accessed through Telnet and this (indirectly) allows the sync rate to be adjusted.  But that's a task for experts and leaving the router on is a far simpler solution.

[#3]

spraxt is right, you need to leave you router/modem powered up at all times. Not very green but the way Max works.
Anthoer thing i found that causes disconnects is having phones on the line without a filter.

[#4]

Many thanks to spraxt and ed for their comments. I will try leaving the router/modem powered up all the time and see what happens (I used to do this anyway - I had just got into the habit lately of turning it off at night).  My connection stabilised quite quickly yesterday morning (at 6400 Kbps) and stayed up all day.  I left the router powered on overnight and when I booted up my PC this morning I had to reconnect to the network, but it reconnected at the same speed (6400 Kbps) and has stayed up all day so far.  I feel a bit daft for raising it in the first place now as it is not really a big deal in the overall scheme of things  - I think I just got a bit fed up one day last week having to reconnect several times. Thanks again for the advice.