Try a few different speed test sites, and if they have more than one location to try from try multiple locations.
I'm on VM 20mb, and have done tests in the past from speedtest.net where it's reckoned my speed from the closest server was about 5mb, from another of their servers about 12mb, and when I did the test on another site i was getting nearly 20mb.
Basically don't trust speed tests too much, they tend to be unreliable*, a better option is to download 2+ (reasonably large 100mb+ each) files from a server that you know is good**, and look at the total download speed you get from that.
IIRC VM have an FTP server from the BlueYonder days that has a lot of games demos and patches on it, which can be a very good indicator of your speed.
*They are trying to work out the speed based on small files being transferred from servers that can be overloaded.
**Remembering that some servers limit your download to them by either connection, or IP (to try and give a reasonable level of service to as many people as possible, rather than letting 5 or 6 people with good connections use up all the servers bandwidth).