When I was planning to move house, I wrote a script to collect as many FTTC predictions as I could, for my target postcodes. That gave me a lot of data, where I had a predicted speed range for each postcode - all from September, using the 8C profiles (capped at 40/15).
I ran the scripts again, to pick up the latest 17A data (capped at 40/20).
From this I have made a couple of graphs showing how the speed figures have changed. I've compared the pairs of figures for the bottom of the range, and the pairs of figures for the top of the range - not perfect, but a good comparison...
Downstream: graph here
Upstream: graph here
Downstream: Where the old predictions were less than 15Mbps, the new ones are roughly double. Where the old were greater than 30, the new are 40. Where the old were between 25 and 30, the new are between 30 and 40.
There is a strange hole for old predictions between 15 and 25Mbps - it seems there weren't any. I'm checking, but this might be an artefact of the fact that my script found ranges of results.
Upstream: Where the old predictions are less than 6Mbps, the new figures are slightly faster - maybe 1Mbps. Where the old predictions were above 7Mbps, the new predictions are almost all for 20Mbps. Inbetween 6 and 7, the new predictions ramp rapidly upwards.