Yeah, the 6141 isn't quite as compatible with Comcast's infrastructure. If you google around you'll find a list of compatible devices and they rate them from 1 to 3 stars. The 6121 rates as 3 stars (so perfectly compatible) while the 6141 ranks as 1 star. Here is the link: http://mydeviceinfo.comcast.net/
Since I don't think Comcast offers anything over 150 Mbps at the moment (I could be wrong, but unless you get FIber to your Home and that uses a different type of equipment) I'd say for the money go with a 6121. They are easy to find and the Surfboard series has always been good. I have one and get over the advertised speeds (I pay for 25 down, 5 up but get 32 down and 7 up). So there you go! As much help as I can give you.