Never liked the additional SSID xfinitywifi that my Comcast router broadcasts. What ever Comcast writes on their site of course it effects my bandwidth and my overall wifi performance. If you login to your customer pages at xfinity.com there is an option to disable it (outlined here). I also disabled my own wifi since the 2.4Ghz band is way to crowded where I live but still the wifi radio is running in the router and quite frankly I don't trust Comcast on this issue. So why not just disable it all together and especially if your not using it? If you are still using any $50 wifi router will give you much better performance so just use that instead!
If you login to your router (in my case 192.168.10.1) and navigate to Connection > WiFi you can see your standard wifi settings. You should currently be on wireless_network_configuration.php if you just change the address and navigate to wireless_network_configuration-1.php you will get much more options to choose from. Here you can select to enable or disable the wifi radio all together and can be sure that it isn't broadcasting any networks any more.
You can also configure transmission power and many other more advance features. What's really interesting here is the two additional "public Wi-Fi" networks that are located on the router. I have more information on them soon so please follow me on Facebook, Twitter, Google+ or just check back shortly for more information about you Comcast Xfinity router.