I'm on the same MB plan and mine varies from 5 to 50Mbps. I really couldn't care less how fast mine is providing I don't get timeouts or the dreaded buffering wheel. What signal do you get on the device?
Yep that was my question as a low signal can have an impact on the speeds as well as congestion. Providing pages are loading and any streaming activity is not buffering I would not concern yourself about the speeds at all.