I recently upgraded to 100Mb/s from 25Mb/s. I am still getting exactly the same peak speed that I had at 25Mb/s. Peek speedtest from comcast and/or other is 33.3Mb/s with the modem (Netgear CM600) directly connected with 1Gb ethernet to the PC. Under most conditions I still get this speed through a netgear DIR-655 and a couple of 1Gb switches.
The one thing that did seem to do something is factory resetting the modem and then activating at www.xfinity.com/activate. Some new downstream channels showed up but the speed is still exactly the same...
Any ideas? Thanks,
P.S. Of course I have experienced the frustration of navigating the the 1-800-xfinity and online trouble shooting to get to the agent who can do the below: