I'm on Comcast Internet. I'm paying for 6 Mbps download speeds and it does sometimes give me steady download speeds averaging about 6M. However they give us 'Speed Boost" also. This allows us to download at a much faster rate for the first 20 megabytes of the download. My downloads often start up at about 16 Mbps. Then after a while they slow down to my usual 6M transfer rate. When I go to the Speakeasy Bandwidth Test it allways says I'm downloading at somewhere between 12m and 16M.
I think Road Runner does something similar. They advertise 7M download speeds so their equivalent to "Speed Boost" might be a little faster than Comcast's.
Please take this as just a guess. I really don't know about Road Runner. I only know my own...