Nowadays even I don't use 40GB (P2P torrents)
It's always far better to start on a low/lower contract, then upgrade at a later date if necessary.
If they can't supply what you have asked for, it could be hard work arguing the fact they are not providing a certain service to get your fee reduced.
Wheras they will soon upgrade you without any problem.
At least that way you will have been able to run the checks needed etc.
Although Kitz has already pointed out the stats (which I don't understand so am saying no more on that subject)
A few months ago, when I was also looking for a new ISP, there only seemed to be 2 that was of interest to me, "BE" and "Sky", unfortunately BE is not in my area, but Sky looked very promising.
The only reason I eventually did not change was because circumstances changed with VM.