Different internet speed testing sites use different ways of checking the internet speed, hence they will all show different results. With that in mind, internet speeds will always vary depending on the number of users on the ISPs exchange, what sort of content you are loading, if you go through a router, what DNS you use, and a lot of other things.
Now for the contention ratio. From Wikipedia:
In computer networking, the contention ratio is the ratio of the potential maximum demand to the actual bandwidth. The higher the contention ratio, the greater the number of users that may be trying to use the actual bandwidth at any one time and, therefore, the lower the effective bandwidth offered, especially at peak times.
Hence a contention ratio of 1:1 means that you are not competing against any other users for your internet. There is really no easy way to prove this at all.
I'm also assuming you have a dedicated T1 (either bonded or non-bonded).