I would say your estimate of length may be a little low. Don't forget to add the rise of teh cable up teh pole, the small extra amounts from pole to pole as it is not taut and horizontal, The underground cables from last pole to the first manhole which could be 1 to 2m down, then possibly a 1m loop in each manhole and then to the original PCP, then the PCP to VDSL cabinet, possibly with some slack too.
Your attenuation suggests maybe mid to high 300s - although it could be due to lighter, finer gauge conductors. For a 14.2 dB attenuation, 88Mbps Max attainable is about right - obviously noise levels can push that up or down.
I am on a line with 16.3 dB attenuation and have a Max attainable of about 79Mbps and it is suggested that at 60Mbps and above 3dB can be worth around 11Mbps, so comparing the two there is around 2dB difference which would suggest somewhere from 6 to 10 Mbps extra so yours ties in fairly well.
M H C
taurus excreta cerebrum vincit