If i bought a car that went upto 80 miles an hour, but I only drive at 50mph, I wouldnt accept that, so why should this be any different? It is different because (extended alanogy) you are buying a car together with a length of road to drive it on. Many cars are quite capable of 80mph on the motorway, but not on a muddy rutted track.
The FTTC infrastructure is capable of 80Mbps, but if you have a long or bad line, then it's not capable of delivering it to you. Broadband connections, like roads, can deteriorate. If they haven't deteriorated too much, Openreach will probably priortise building more over fixing yours.
I had a similar thing with dropped speed when I was on BE. Almost all the time I had speeds around 18-20. At one period it dropped to 15 or so for several months, because of noise that happened every morning around 8:00am. We never traced the noise, and after a few months it went away and my speed increased again. If I bothered to resync after the noise burst finished (around 9:00) I could get higher speeds for the rest of the day, and then the line would be dropped next day around 8:00 and resync at 16. With infinity you don't get the option to get the higher speed while available, because DLM is determined to give you a stable connection. Also with Inifinity, unless you get an unlocked modem you won't be able to see if that is what is happening.
As a matter of interest, what was your estimated speed? If you can't remember, look it up at http://www.productsandservices.bt.com/products/broadband/internet-speed-test .
Talking of noise on the line, there seems to be some noise on this forum thread line ....
I get the analogy, but it has been fast and fine and dandy for nearly 2 years -maybe i am bit too naive, but i havent touched my muddy track. Maybe it is noise on the line, but it passes a line noise test.
You pose a good question about estimation, if i remember rightly it was projected that i would get around 55meg, but i got 68-70, ironically it is now synching about 55meg and i get 50meg down.
Thanks for the reply.
Roger and Bullitt - advice when sincere is greatly appreciated. Without that the forum would be useless. I am in the hands of others for guidance, so unfortunately I have to take the rough with the smooth.