We all make those mistakes, damn you B b!
Anyway from what I have learned (based on line speeds reading as Max/attainable and achieved/set/profile):
VDSL will get 100% sync rates within 600-1000m copper... AKA short range BB
ADSL is long range BB (max attenuation (loss of speed)) is at about 6.5km
VDSL cabs (two sizes 5ft tall two door and 3/4ft tall single door) can have 96 circuits at either 2/40 or 10/40. These can be BT retail sold to you as "infinity" or sub loop unbundling (the loops from your cab to house) where other ISPs rent the DSLAM to give you service.
VDSL cabs must be situated within 100m of a cab and must have mains power else no cab. They don't need PP the max time it takes from proposal to install start is 55 days I believe.
MOST urban cabs are within 1000km of line (line follows roads and comes up your pole... include this to estimate your length to cab). Cul-de-sac is not going to be good for you if it loops in on itself, i know the road near mine at the start they get 10/40 at the end (approx 30 detached houses) he only gets 5.7/22 (still better than his prior 0.1up/0.4down)!.
So far 60% of FTTC installs sync at 100% and 90% achieve a sync of over 30mb down. This information is from approx nov/dec 2011 and is obviously the data for the first installs since Jan of that year (still amazingly better than prior ADSL sync speeds where 50% is lucky!)
The actual sync rates always turn out at 1999 or 10000 for up and 39998 39999 or 40000 for down, no idea why this is what I was told.
ALL FTTC CIRCUITS WITH A WHITE OPENREACH MODEM are the ONLY broadband in the country with a MIN down speed, 15mb. If your line is greater than 1km from the cab you might get about 10-14 mb if its about 1.4km, in this situation your ADSL is likely to be less than 2mb anyway so there is an option:
The ISP may offer to serve you a "sub 15 meg" product, this is individual to ISPS, I know in the case of BT retail Infinity option 3 is cheaper, others no idea.
The purpose of the white modem is so Openreach (the company that own the wires from exchanges therefore through cabs and the cabs themselves) can guarrente that their engineer did a managed install. This is merely putting the NTE and VDSL modem at the FIRST socket in the house (aka before your demarcation point, any internal wiring you do can not mess up the line, they know its a direct, a-b leg with no star wiring and no faulty connectors)
THIS is why they can give you a 15 meg guarantee. The VDSL modem is the DSL demarcation point and they will pay for its maintenance provided your little angels don't facilitate its demise.
Now the people who currently install these VDSL modems for ISPs come in three flavors. BB openreach engineers who have done the training for FTTC. Openreach apprentices who have been trained to do the job and are now doing college work on the side. The last are... contractors... in my area by the name of "kellys", if anyone is working "on behalf of" openreach... watch them. I will not spread bad blood, just watch them and all should be fine. These are the guys who i have seen people in the BT infinity thread quoting saying "I had no idea they were increasing the speed".
On to the increased speed. When the VDSL cards in the DSLAMS in your local fibre PCP (cab) are changed to 17a the max rate will be somewhere in the 120meg region if you are in idea line conditions.
NOTE: at higher speeds (frequencies) there will become more disparity in line sync rates, at the moment vdls 8a (10/40) is nothing compared to 30 (200meg down) that could be used, its just not been tested or approved yet.
Well that's my ramble, might edit it later to make it more readable
) hacking it is the only way to see early if your cab has the tech in it
as i don't have a cab 
Will do some testing as sono as we get it 
