The age/condition of your line affects the actual speed you will get, not just the distance from the cab, the checkers cannot really allow for this.
As the line ages and gets damaged by weather, the speed slowly drops, although speeds anywhere near those quoted by BT would make everything seem turbo boosted in comparison to ADSL.
Just be aware that not all VDSL packages are the same, some cheaper ones limit your upload speed severely; now you may not think you need a good upload speed, but when you try to send Grandma that 500MB folder of baby photos with a 2Mbps upload, you suddenly feel like you are back in the stone age.
Just remember to factor in line rental, the big boys all charge big money, so the smaller ISPs LOOK poor value, but their often cheaper line rental means they are usually only a few £ more overall - and can work out cheaper at the end of the month, due to BTs extortionist call charges.