Dear @Dave67 ,

Thank you so much for taking the time to report the issue to our community!

If you choose Dynamic IP in WAN connection type, what is the WAN IP address?

What is the firmware version of ER7206?

Did you use the router in standalone mode or controller mode?

You may try to reset it and test again.

  @Dave67 

It's probably one or two things. 

First thing is you need to make sure you are using Comcast's speedtest server, and if the reported performance is better than a 3rd party via Ookla then you know that they have an oversubscription between their internet pipe and all their own feeder pipes coming from fine people like you.

Second, coax is a shared media access technology, meaning you and all your neighbours share the upload and download channels, so it's entirely possible that your local cable system is just 'maxed' out--especially in these days of 'work from home'.  To fix this Comcast needs to do a 'mid-split', where they break your neighbourhood cable plant into two or more segments, each independently fed from upstream (so each segment gets its own fresh set of u/d channels).

My advice, unless boiling oceans is your thing, if you can only realistically get 300-400Mbps is to only pay for that much, so do they have a cheaper 300M or 500M offering?

  @Dave67 

That's fantastic news!  I hope that defective cable was 'recycled' in a manner consistent with the grief it caused :)

A single copper GigE port should be able to get upwards of ~950Mbps assuming optimal conditions.  I am not surprised that bonding the two ports did nothing as a result, since you were not exceeding the capabilities of a single port.  I could see it making sense if the internal DOCSIS modem was capable of and provisioned > 1Gbps and you needed the two ports bonded to allow that out of the modem (as presumably the MB8611 could be).  My personal DOCSIS provider also allows bursts above the stated rate before the shaper kicks in...I think this is because the number and capacity of RF channels being used by the modem is greater than your 'subscribed' rate.  Let's say you were using 5 downstream channels, each capable of 180Mbps...that up to 900M of capacity, but the traffic shaper upstream would try to slow (throttle) you back down to ~800M within a few seconds of any sustained burst exceeding 800M. 

Of interest but mostly irrelevant to you is that I also have a FTTH provider and what's interesting about that one was the ability to establish a second connection through the first one (ie use the provider's FTTH modem, and then using an ER605 behind that to setup a second PPPoe connection...and that second connection could burst up to the capability of the ONT (~1Gps symmetrical in my case), whereas the outer connection seemed to be limited to my subscribed rate).  Fun and games.