I am looking to buy a modem instead of renting. I am only on the 60Mbs plan and even if we upgraded, it would probably only be to the 75Mbs one. We are not too speed demanding as the most we do is maybe two 1080 streams at a time or one 4K stream while browsing websites. We stream music through our unlimited phone plans. So, it looks to me that an 8x4 would likely be just fine for our needs, but wanted a more expert opinion.
As for the router, I plan to go high end there as I do have needs for internal data to be at high speed for RAW image file sharing from a netwoked drive to a laptop and casting Xbox to a laptop.
An 8x4 will suffice but more are better. It's not just about one's subscribed to speed tier. It's also about having a fatter pipe to the internet / more available shared bandwidth to help mitigate congestion on your local cable segment so that everyone can get their subscribed to speeds more consistently. Especially during peak usage times.
I live in a fairly sparse area. For example, our neighborhood is able to have about 80-100 homes built and there are about 20. Of those not all have Xfinity. I can get a 16x4 for only about $15 more, so I am kind of leaning towards that. They gave us a 24x8 unit for the rental, which I am certain is overkill for the speed we pay for.
If you're putting the money into buying the modem you should consider these things live for 5+ years typically and with 3.1 being rolled out it's better to future proof yourself instead of a year down the line needing to upgrade again if Comcast EOL's your modem. There's a promo through the end of the year on some new gear.
https://www.xfinity.com/support/account/voice-internet-manufacturer-promotions/ (expiring 12/31/2017)
I just went with the MB8600 through Amazon with discount put it at ~$145 and it's a full 32x8 rated up to a gig and expandable to 4 gig service through bundling the ports when the service becomes available. Currently there's only 3 available 3.1 modems on the market and they're all about the same price but, it comes down to the chipset inside the modem and the expansion ports for the future.
I checked it from the post and it doesn't work but,
does work logged in and incognito as well.