I just replaced my Comcast provided modem with a Netgear CV1000, which is a docsis 3.1 model. I'm continuing to use my own separate Netgear router. Connected to the latter with Supra Ethernet cable is a Google mesh network with a total of 3 access points.
Before swapping out the Comcast unit, I checked the speed: 290 Mbps (I pay for 300). After replacement with the Netgear unit, my speed is 90 Mbps. Still fast enough for 4k streaming, but certainly a lot slower than it was. Funny thing is, my signal strength is very good, somewhat better than before. I had to have Comcast CS assist with getting the new modem online, ran into a hard stop with their app. Wondering if another call to them could improve my speed...