Different modems can use different numbers of DOCSIS channels. A 4x4 DOCSIS 3 modem is only capable of, at most, 150Mbps and on average 75-100Mbps. A new DOCSIS 3.1 model can do >1.2Gbps.
3.0 spec does up to 1.2Gbit/sec, just like Comcast. You know up to 200Mbit/sec, which is more like 20 because of all the "extreme complexities of the internet service".
DOCSIS 3.0 supports 38Mbps per channel, which is in the table on wikipedia. Not every modem is capable of 1.2Gbps - The fanciest modem out there is 32 channels, which gets to your theoretical 1.2Gbps. If you have a 4 channel modem and expect consistent speeds of more than 100Mbps, you are SOL.
https://en.wikipedia.org/wiki/DOCSIS
3.0 spec does up to 1.2Gbit/sec, just like Comcast. You know up to 200Mbit/sec, which is more like 20 because of all the "extreme complexities of the internet service".