The speed is nice, but that 6mbps down is a max speed, and the burst rate is nothing to go as it's just that: a burst. The only thing worth the cost would be the 2MB upload. Even e-mailers and web browsers will notice that improvement.
That said, Comcast has been known recently for pulling a "morality" stunt by blocking BitTorrent, a peer-to-peer technology. I'd leave them for that alone.
That said, if you have the ability to go fiber optic, I highly recommend it.