I do believe that your OS DNS servers have priority. I run mine through the CGN3 but I'm looking at reinstalling DNSCrypt to encrypt DNS data. If you do a search in Windows Help and Support for "Change TCP/IP settings" and follow the settings instructions you will see that selecting the DNS source in the OS will over-ride the router feed for DNS addressing.
The other consideration is that by placing your DNS address on your pc and laptop, even if your router is ever hacked, and the DNS address is changed, you still have control over what address source is actually used, which in this case is within the PC or laptop. A key consideration in the event of hacking.
I'm not sure what happens when you have two routers in line followed by the pc, but from what I remember, there should be a selection on the second router to obtain the DNS source from the default gateway. Say for example you had the CGN3 in gateway mode followed by the N66U, followed by the PC or laptop. If the selection for using the default gateway DNS wasn't checked in the second router (N66U), then the DNS addressed would come from that second router. If you then decided to use the address within the OS, then any DNS address in either router should be ignored.
I've used Steve Gibson's benchmark tool before and from the site page comes the following:
When the Benchmark is started in its default configuration, it identifies all DNS nameservers the user's system is currently configured to use and adds them to its built-in list of publicly available “alternative” nameservers.
So, in order to rank your current DNS nameserver, you would have to set it to a legitimate server address, either in the routers or in the OS.
