I called up to have my speeds increased to Ultra in Northeastern MA. They said no problem, but my SB5100 wasn't going to work and I needed a new modem. They sent me a SB6120 DOCSIS 3 modem via UPS the next day as part of a self-install kit.
I did reboot my 5100 and get provisioned for Ultra according to the modem log, but it was maxing out at around 20/2 using the Comcast test site. I saw no powerboost. With the new D3 modem, I am seeing 30+ on powerboost down and a steady 5 up. The new modem definitely makes a difference.
The modem has a gigabit ethernet port and also shows channel bonding for download. Upload speed is single channel.
It's quite fast. I was able to get 9GB (yes GB) downloaded in about 50 mins downloading some video. It's really REALLY easy to hit the cap with this thing now if you're a heavy downloader.
Finally made it to the nearest Comcast office today (Wheat Ridge) and the only modem they had was an RCA unit. Didn't pay attention to the model number, but it was in new packaging. Any ideas on the specs of that modem? Anyhow, I returned my WebStar (seems like my Zoom 5241 works fine now) and asked about DOCSIS 3. They've heard nothing :/
I'll bet even if it does come here pricing will be absolutely outrageous for the 22/5 tier, since Qwest's current 20/896 setup is speed-wise similar to 16/2 from Comcast, except with much slower uploads. Grr...
EDIT: According to some quick searching, the cable modem they had was the RCA DCM425. Looks like it's just as cheap as the WebSTAR...