How did it all pan out in the end then ?

My contention point was that N businesses supplied over a 1M leased line will see more contention in practice than the same number of businesses on 20:1 contended ADSL from BT.

If there is a 1M line only one person can get 1M, and then with no other traffic. Add one guy streaming radio and nobody can get 1M. On a BT exchange there is say 10M of backhaul serving the 20:1 users, so you can have 10 people getting their full 1M worth before the 11th guy slows everyone down a bit.

The contention may be the same at 20:1, but the probability of seeing that contention rises exponentially as the service supplied approaches the backhaul capacity.

Phil