You are correct,the DLM does not seem to raise the profile levels,you have the same problem as me except that mine has not changed in over 6 weeks now,it was 77.41 for nearly 18 months now it is stuck at 47.41 and the strange thing is that my estimate is now also 47.41.
We are being controlled and conned.
There are lots of reasons your speed may change, and many of these will be permament. There may be slight degradation in the line, or extra installations of FTTC may have caused crosstalk and lowered the speed attainable. Where the drop is trivial as in your case, just accept it. (I guess you are still well above the estimated speed anyway?). Even in much more extreme cases such as ironman's it seems almost impossible to get things sorted out properly.
While hoping for an increase, disconnect and reconnect the router each morning (best done from the web interface) in case DLM has raised your sync speed but the IP Profile has not been adjusted appropriately. This happens when the modem resync is so fast that the higher level PPPoE connection is not broken. As others have said, do NOT do anything to the modem.
Do a factory reset of the homehub by pressing a pin into the recess button on the rear for about 20 seconds.
Disconnect. Once disconnected, the button will become 'connect' or 'reconnect' so you need to press a second time.
Reset or restart or sticking a pin in will be ok, they will make the router do much more and take more time. For some router errors that is necessary, but for refreshing the IP Profile disconnect/reconnect is the quickest.
The reason for doing the reset each morning is that if DLM does allow a speed increase it will usually action it in the middle of the night to minimize disruption.