I have a Cisco DPC3008 modem and a Belkin N600 DB router to have wireless connection in my house. I also use ethernet cables from the LAN ports on the router to connect my Xbox, PC and Wii U to the internet.
Yeah don't enable Intellistream. Basically what is supposed to do is give your devices equal upload and download speeds so that not one device has the upper hand on download/upload but in fact it's really a lousy feature that will cause you to get slow speeds. Sometimes the speedtest feature that is supposed to measure ping, upload and download won't even work. When I did run it one time it gave upload and download speed of 10mbps. Basically it's supposed to be a traffic control for your router but it definitely slows performance so don't use it
I also have an N600 DB router, and yesterday got the call that Triple Play customers like myself have been automatically upgraded to 105 Mbps in my area. I did all the modem reset that was instructed, and was disappointed to see my speeds still capped out at 20 Mbps. I was supposed to have been at 35 Mbps before! I would point out that you can do a speed test using http://speedtest.net/ or http://speedtest.comcast.net/, and manually enter those numbers on the Intellistream configuration screen. Do make sure to have Intellistream disabled before you run the tests. In my use of those services, I saw up to 91 Mbps up/25 Mbps down yesterday and earlier this morning. It varies considerably, though. Right now I'm seeing 38 Mbps up/20 Mbps down. In the end, I'm disabling the Intellistream QoS feature. It might make sense in some households, but in mine I don't think it matters. I don't like wondering if my router is somehow throttling me.