When Comcast gives you a speed rating, often you will achieve higher than that rating. For example, my line is rated at 50 down and 10 up. Here is my latest speed test:
As far as peak time speeds, my download usually remains 55 or above and my upload is always above 10.5.
In terms or reliability, I have had some problems in my area, but, it was not Comcast's fault. There was someone stealing the amplifiers in the neighborhood. The delay in getting it fixed was in Comcast coming out and replacing the amplifier.