Connected to O2 now, seems to work great. Browsing speed not discernible from 50Mbit cable.
Bandwidth (Up/Down) [kbps/kbps]: 1,304 / 16,827
Line Attenuation (Up/Down) [dB]: 13.5 / 28.0
Line is about 1.9km long.
Costing me nothing for 2 months and getting 100 Great British Pounds cashback so the year where I'm under contract will not cost me very much at all
Going to switch to Annex M once the line has settled down which will give me an upstream around the 2.2Mbit mark as a guesstimate.
50Mbit is still under contract but, barring serious issues with O2 or VM pulling their finger out of their arse, will be heavily downgraded or removed entirely as soon as the contract is up. Not a heavy newsgroups user, which seems the major reason for having it, so finding very few reasons to keep it given stability concerns, traffic shaping concerns, poor upstream, etc.