I did not have performance issues. The old firmware worked fine with the Comcast infrastructure.
What I had were stability issues. The cable modem would lock-up and I would have to go hit the reset button every few weeks. (A flight of stairs, two doors, a rack door, squinting to find the little recessed reset button)
I wanted to get the new firmware in the hope it would be more stable. Often a slow memory leak in a process is all it takes to be the achillies heel of an otherwise great product.