So this means I could be affected by crosstalk.....meaning that the speed I initially get could drop as more people go live on my cabinet? Crosstalk...noise?
Yes - the speed you get initially can drop as more people get onto the cabinet. And yes, to each modem, the crosstalk from other modems is considered as noise.
Here's my personal experience:
My current line is 400 metres, with an estimate of 55/18. It initially achieved 80/20, with maximum attainable speeds of 88/26 (reported by the modem). Over 18 months, the crosstalk has increased, and the modem now reports attainable speeds of 72/25.
What sort of effect is it likely to have...i.e. big speed drop?
Crosstalk is a funny beast, and depends more on how close the copper pairs are within the cable, for how far, and how accurate the twists are - which ultimately depends on the manufacturing process.
It also depends on which exact pairs carry VDSL, so ultimately it depends on which other subscribers take an FTTC service.
So the impact is random.
The actual effect can come in two ways - it either appears as noise, which causes your modem to sync at a lower speed, or it appears as interference that causes data errors. If enough errors happen, DLM will intervene to add FEC & interleaving (which affects both speed and latency) or adds banding too (which further affects speed).
So, my estimate is about 28mbs,
BT's estimate already takes into account a reasonable worst-case for crosstalk on a line that otherwise works OK.
So while you may see a speed drop from your initial connection speed, that initial speed should be higher than the prediction (as an early adopter) and it ought to eventually drop to somewhere near the prediction.
Some lines have faults that mean they don't hit the prediction, but that is a different ballgame.