DOCSIS 3.0 channels

I recently upgraded my internet to Performance Pro 300/10 service. My current modem/router (Motorola SBG6580 )still works. However, I have run speed tests from numerous sites and the download speed varied from 128Mbps -275Mbps. I am looking to upgrade my modem/router combo. How many DOCSIS 3.0 up/down channels does Xfinity use? I don't want to pay for more if they will not be used.