Thanks for the replies.
Does crosstalk affect the higher frequencies more?
I recall I used to sync around 60 MBps around 9 years ago then over the years gradually decreased to around 40 Mbps. I even had a pair swap after much effort.
Higher frequencies are always affected more by noise as they are harder to hear, and cross talk is just noise, also it isn't just about noise, often your modem might start using a lower power for various reasons, perhaps because it is disturbing someone else badly. You need to know historically what power your modem was transmitting and receiving at over the years to get a better picture of what the changes are.
At the end of the day there is very little you can do about crosstalk or general noise and most people have seen their VDSL connects get slower unless they had tonnes of margin at the start being very close to the cab. For example when I was on VDSL my margin was around 8db (reduced from 10 when I first went live), during a power-cut it shot up to 15db because everyone was knocked off apart from me on a UPS, so cross talk accounted for 7 or 8db of loss.
Regards
Phil