Just going to throw this out there for discussion.
I lent a friend of mine my spare BT 2V modem to see if it increased his sync speed.
He's been on FTTC since last year, about 400 to 500m from the cab with an IP profile of about 33000 or so.
Everything seemed the same after connecting up the new modem but suddenly after almost 2 weeks he ran the BT speedtest, now his IP profile is 38717 / 10000!
I'm not drawing any conclusions but the facts are interesting.