Infinity speed drop

I've had Infinity since November 2011, with a speed of just under 38Mb on installation, 71Mb on the switch to 80/20. In the last month I've seen about 8Mb lopped off, and today I find I'm on a profile of just 38.4Mb. Basically back to where I was on installation. Is there any point in raising this with BT, or will I just get fobbed off with what I have now being good enough?

Unfortunately I don't have a flashed modem, so I have no line stats. It never seemed worth the effort given that it just worked. I expected to see some speed loss due to crosstalk, but this seems way beyond that.

Have you rebooted the Openreach modem during daylight hours to see if the speed recovers.

DSL modems will only sync to lower speeds if there is noise issues, but once the noise goes they do not automatically reconnect at the higher speeds.

I did after doing the BTW performance test, yes. Are profile changes any quicker now?

With WBC and FTTC they are immediate and are a simple formula based on sync speed rather than bands now

Thanks, checked again, and it's jumped back to a profile of 65.52Mb. Around 9Mb shy of the initial 80/20 upgrade high, but I can live with that.