The upstream is about T1 speed.
It is not dedicated per say(as an actual dedicated line is run from your house to the phone company's main hub apart from telephone line), but they do guarantee your speed unlike cable. I have a seperate line from the box to my router. And the speed never varies. I get better performance with this than I would with a T1. I had a friend who had a T1 at his office that was closer to the hub than me, and I was getting better speed with a 768 at the time than he did with a T1.