Kushan is right, you only really know when you are checking the speeds in your locality, ideally your street.
We have a long running issue with utilisation (3yrs+) but I think nowadays we are in a distinct minority. Most VM customers get a good service I believe.
On the day of installation, make sure the Engineer shows you your (Cable Modem) power levels. It is important this are within certain ranges otherwise you will get problems, as a reference here are the levels you need to have:
http://community.virginmedia.com/t5/...4/td-p/2271297
Last thing: I think you have 28 days (?) to opt out of the contract if you are unlucky and find you are in a over utilised area. I do think you should be ok though ..
Last last thing: make sure the Engineer gives you the Superhub 2 AC. I think these are std kit now but double check ..