Now DTMF that is not totally true. You pay for what speed you want. Not sure if it has changed but when cable modems first came out it was a shared connection. You share the bandwith with the number of users online at the same time. So at times it could be super fast(3am) or real slow (6-7pm), but that may have changed. Speed comes down to the website your trying to access and thier upload speed. If your provider only has a T1 to the backbone then your not getting any faster than that. However if they have a fiber connection and only 1 hop to the backbone then you will have much higher speeds. I wouldn't base my decision on speed but on Reliablity-how often will you be down? That is what really matters.
Good Luck