"As has been mentioned previously, the BT Openreach estimator that's available to wholesale suppliers is pretty accurate."
The speed I'm able to get in the middle of the afternoon here might be a good deal more than what I'd get in the evening if a lot of people down the road start streaming stuff when they get home from work and my bits have to share the infrastructure with whole lot of others. It might also be better or worse than my neighbours; all our connections come from the same point on the buried cable. Mine comes underground, theirs are overhead from a cable running up a pole, some of them distributed direct from that pole and others from a second pole linked to the first. Clearly there are various options for water penetration, different wiring choices (Al vs Cu) etc.