Since I can't reply to the other thread with similar description, have to make a new one.
Issue is with this gateway (xfi CGM4140COM), when you run in normal router mode I get 800-900 speeds (normal)
When I enable bridge mode max speed tops out 650 or less.
I've tried directly connected to PC in bridge mode same thing 650 or less, tried through my Gigabit Router RT-AC68U, tops out 650 or less.
There is something wrong with this gateway, firmware or whatever there are many others complaining about the same thing. Only solution is to get your own docsis 3.1 modem, so you can use your own router in order to get gigabit speeds.
However that would cost me another $25 a month to get the unlimited data cap.
I've also tested putting the xfi Gateway CGM4140COM in DMZ then connecting my router, and of course works fine i get 800-900+ speeds just fine. However double NAT is a problem, and not a real solution.
Can someone at comcast/xfinity look into this and fix it? Its not just me there are many others.
Many other threads about this.
I literally was having the same issue for the first two weeks of being on the gigabit plan. I've just been pouring money into getting it closer to subscribed speeds. I was following the original thread you mentioned for a week.
After being lied to, apparently by the customer service rep that i spoke with initially (when I called and got the plan upgraded). Guy told me I couldn't use a third party modem, without paying more! Which I thought was CRAZY. I've always owned my own modem and have been with comcast for 6+ years.
Anywho, XB6-T was terrible, I had never seen gigabit speeds directly wired to the modem. The modem could be in bridge or non-bridge, I would only see 600-650 mbps with speedtest app on windows 10 (not browser version of speedtest). Yesterday, I bit the bullet and went to bestbuy and purchased a NetGear CM1150v, since I had great results with my previous 500 plan with a CM1000. Night and day difference between XB6-T and CM1150v. I'm consistantly getting 960/43. Both tests on XB6-T and CM1150v were both from same speedtest servers. I'd say save yourself the headache and purchase a thirdparty modem, anything that's not a XB6.
edit: When I spoke with a live agent today, she mentioned that, I would not get charged extra for having my own modem. Matter of fact I would be saying 14 dollars. Same as my previous agreement. I'm not sure whos lying between these two agents, lol...
No, it is normally 50$ for unlimited, or 25$ for modem+unlimated. I mean at this point I rather just be paying the +25$ more to have consistent internet.