One does not want to be accused of over stating the speeds, though we do get some strident campaigning to say the figures are still too high.
If you are aiming to show estimates that represent the bottom end, wouldn't it be better to give the column a title that reflected this? Rather than just an estimate? Perhaps a "minimum estimate"?
BT produce a range derived from the 20th and 80th percentiles, but fail to tell anyone what the range actually represents; because the bottom of the range is still only the 20th percentile, some people could be below the minimum...
Given that BT show a range, would it be better for TBB to also have a range, but to go on and explain why there is a range (crosstalk), and how you can expect variation?
I like the way in which the Broadband Forum's document on vectoring shows speeds vs distance - which distinguishes what people can normally get vs the worst case and vs the best case vs the vectored case.
See figure 6 in
http://www.broadband-forum.org/marketing/download/mk...
Essentially, the blue crosses there represent the same kind of thing as BT's 20th and 80th percentiles. I'm not trying to say anything about vectoring here ... just that the depiction of the "normal" by the blue crosses is actually useful.
That graph represents a 17a profile that looks very similar to BT's 998ADE17, but on 0.4mm copper; it probably understates the average line capability in the UK. Unfortunately, it only goes up to 1,000 metres.
I have seen similar graphs go up to 2,000 metres, here:
http://cms.comsoc.org/SiteGen/Uploads/Public/Docs_Gl...
Pages 10-11.
Unfortunately, those graphs are for the 17a profile known as 998E17 profile - which differs from ours considerably: there is no US0, so it has limited upstream range; and 2MHz is swapped from DS to US (the 12MHz-14MHz portion), so at closer distances, the DS speeds appear low compared to the UK, while the close US speeds look high.
On the positive side, the graphs use TP100 cable, which is 0.5mm solid copper, PE insulated, multi-pair cable as used in BT's D-side. That part ought to match up fairly well.
Overall, perhaps the longer-range part of the downstream graph (1km-2km) ought to be similar to the UK experience.