There has been some general discussion regarding how a user's FTTC IP Profile / BRAS Rate is calculated.
Having studied a number of FTTC connection stats, it appears that the new(ish) 88.2% quantisation method for calculating ADSL IP Profiles does not apply to FTTC connections.
It would appear that FTTC IP Profiles are typically calculated to be approximately 96.79% of DS Sync speed.
Users with unlocked FTTC modems will be able to see their Sync speed & calculate their IP profile, double-checking it against the IP Profle as reported in BT's usual speed/performance tester.
However, users with locked modems have no real idea of their Sync speed.
e.g. a typical IP Profile / BRAS Rate for a user achieving the full 40Mb sync speed would be in the region of 38715K (96.79% of 39999K).
My own connection is currently Synced at 28839K, the reported IP Profile / BRAS Rate is 27914 K.
Again, the IP Profile is approximately 96.79% of sync speed.
Conversely, DS Sync speed can be calculated as approximately 103.3% of IP Profile.
As an aside, my DS throughput (when not affected by contention etc.), as reported by speedtest.net, is usually around 97% of my IP Profile / BRAS Rate:-
My connection wasn't initially affected by contention, regardless of the time of day or night, but I have recently noticed DS throughput speeds typically reducing by 3 or 4 Mb or so at peak evening periods:-
Paul.