DOCSIS 3.0 channels

The SBG6580 is VERY outdated and not capable of 300Mbit speeds. It's only good to 343 THEORETICALLY, but the actual speeds will be lower due to overhead. It's only an 8-channel modem. Comcast supports up to 32 DOCSIS 3 channels, and also supports OFDM in DOCSIS 3.1 in most areas. You can find some user-owned gateways (modem/router combo),, or you can rent the Comcast gateway. Most experts would say to get a separate modem and router. This gives you more flexibility as your own router will often offer more features and it's settings and firmware will not be controlled by Comcast.

Also forgot to mention it's only 802.11n (now called WiFi 4), which is very outdated, too. Most newer gateways/routers support at least 802.11ac (WiFi 5), and most likely now 802.11ax (WiFi 6), and even WiFi6E (WiFi 6 with extra frequencies).

@user_d2478c 

Look here for compatible devices: https://www.xfinity.com/support/devices 

The modem will use all the DOCSIS 3.0 QAM and DOCSIS 3.1 OFDM channels it can.  Your plan just determines how much of that bandwidth Comcast lets you use.  Most of the time it doesn't make a difference but having a 3.1 modem in a congestion situation could let you sidestep everyone else on your cable segment by using the OFDM channel.  The catch is that it doesn't help at 300Mbps if you don't have congestion problems.  So if you're getting 300 all day and them evening rolls around and wham you're at 100-200 more channels might help.  Other than that extra channels are basically just future proofing, though Comcast does to speed increases periodically and eventually they'll kick all the DOCSIS 3.0 equipment off and require 3.1.

126-275 seems reasonable for a lot of 802.11n WiFi routers.  You might get a little more on a wired connection, but you're doing well just getting 275 close to the router with that gear.  Nice to see someone on here with gear that's just old and not having a real problem.

It's hard to make any suggestions about specific models or what you should do without knowing more about your devices, usage patterns, and home layout.  It's mostly about WiFi, like do you have any use for WiFi faster than your internet connection and figuring out how many access points will it take to provide decent WiFi coverage in your home.