After a bit of a journey I'm now on VDSL ;-) Day 2 and this is how it's looking. Overall very happy! Of course I can't resist any excuse for bit more tinkering, so:
I'd previously installed a master filter on the corner of the house closest to the road and put the modem in there too, so pretty much taken all house wiring out of the equation. The last 2 things I'm wondering is:
1) How likely is replacing the cable from road to house to make a difference (it's <10 metres)
2) Is the cable used to connect modem to master socket likely to make any difference?