1000m line length is significant because ADSL2+ is faster at that point.
Wrong, it's just above.
It's about 26.5Mbps FTTC, I would know my line is basically 1000m. 🙂
1200+ when it hits top ADSL speeds.
Vectoring is a piece of hardware that helps prevent crosstalk, it also has it's own software which is rumoured to make a line run better with the DLM and able to record more faults remotely (rumoured).
Surely with the self install they will still need a BT engineer to connect the user from the PCP to the DSLAM cabinet???
a link with bit more information on vectoring http://www.pcworld.com/article/2035767/vsdl2-on-steroids-takes-off-as-broadband-over-copper-declines...
In relation to the comment about ADSL2+ and VDSL speed at distances > 1 km...
A VDSL connection is essentially made up of many carriers of signal (DMT modulation) 4khz wide, think of them as channels on a TV.
imagine the more channels you can recieve the higher the speed in total you will get.
The lower frequency channels (used by ADSL2+ and VDSL) can travel further down the line with attenuating (degrading) due to noise etc.
This is also a general rule for radiowaves, the lower the frequency the easier the signal can travel through walls and other obsticales without issues.
So ADSL2+ and VDSL share the benifits of the lower frequency channels, and therefore > 1km the effect should be roughly the same.
However VDSL attempts to use 17Mhz worth of these channels accross the spectrum (hence 17a), as you go up the frequency spectrum the high frequency signals will either pass the grade or not (thats what the Target SNR -signal to noise ratio is for), and if so will contribute to your final connection speed.
All very clever, but its important to note that VDSL is basically very simular to ADSL2+ technically.
Hope I didnt send you off to sleep.
Source: my head but for backup... http://computer.howstuffworks.com/vdsl4.htm