In terms of CPU and RAM usage, there are rapid changes over short periods of time, and data sampling for WebUI representation may not provide representative results about actual CPU load.
To get a better picture about CPU and memory usage, I would suggest to install htop. This is dome over SSH with the following commands:
For your DNS propagation issue, you can add additional option to dnsmasq configuration, to use all available DNS server, rather that based on the currently used interface. The reply from the server which answers first will be returned to the original requester. To do this access router over SSH again, enter the command below:
Press letter i to enable editing and add the following option at the bottom of dnsmasq configuration:
Once done press Esc, then enter :wq and press Enter. Then execute the following command:
- /etc/init.d/network restart
"I wonder if the Modem Category is making the difference in my case."
It should. The fact that Cat 6 modem RUTX11 comes equipped with support two band carrier aggregation should already provide an improvement. The modem is also capable to maintain connection under worse signal conditions and achieves better speeds in general. Though, if your goal is still 20 active users, the bandwidth achieved may still not be sufficient to provide acceptable performance for everyone.