There have been several references and posts, including one from myself, wanting to know if the Stable Rate you have achieved at the end of the 10 day Trial in any way limits your future possible speed if your line/system improves.
No-one seemed able to confirm what the position was. I was given this response from CS.
The maximum stable rate is the lowest speed you sync at during the 10 days and is used for determining faults only.
The actual speed of the connection is controlled by the delta report generated by BT 4 times per day that is monitoring your sync speeds. If your modem syncs lower than (your Maximum Stable Rate) the delta report will slow the through put, if the modem syncs higher the delta report will increase the speed.
This will take place constantly for as long as you have MAX DSL.
Please be aware however that the speed can drop on a daily basis but for the speed to increase again the modem must sync at a higher speed for 3 days.
The Trial period giving a lower Speed than 'appropriate' seems not to be the concern it could have been.
It appears your speed can increase after the expiration of the 10 day Trial provided you synch at a higher speed for at least 3 days.
The Trial would seem not to be a limiting factor in terms of what speeds you can achieve in the future so long as you can maintain synch.