Speed really depends on a few things. First is how much they alot you for speed. Second is how busy the path is you're using, which can change for every data packed. Third is how much bandwidth is avaiable on the other end and how much is being used. With cable, if alot of people are watching tv, it will slow down.
That being said, I've had up to 2mbps and as low as 5kbps. I was going to set up a web server for images but RR has only like 56k up.