Just to add some additional testing I did late last night. I tried my AC1900 router again, after factory resetting it. Connected it to the SB8200 modem and rebooted the modem. This time, I had ~900Mbps download speeds going through the AC1900 router, with my wired laptop!
I then tried to switch it over to my AC3100 router, without rebooting the modem, but my router had a WAN error that said "Your ISP's DHCP does not function properly". So, I rebooted the modem and the AC3100 router, and let it all come back up and online. I then had ~900Mbps download through my AC3100 router. At that point it was after midnight and I went to bed, hoping for the best.
However, I got up this morning and everything was back to ~30Mbps download 😞 Several modem reboots already and no change, ~30Mbps download.
You have to reboot the modem each time you change the WAN connected device, or it won't work. Rebooting the modem allows the new MAC ID of the other device to reach out via DHCP to get an IP address. Try connecting your laptop direct to the modem,. reboot the modem so the laptop can get an IP address, ensure both wireless routers are powered down, or disable wifi on the laptop so it doesn't try a wireless connection, even though your connected via ethernet and run the speed tests, and it should look good.
Wireless 2.4 GHZ on 500 mb down, 50 up - https://www.speedtest.net/result/14979584181\
Wireless 5 GHZ https://www.speedtest.net/result/14979590535
Can't give you ethernet, main computer is crunching a blu-ray dvd for my plex
I have done exactly that process countless times and almost always get ~30Mbps download speeds (as detailed in my original post).
I tried a cable swap from router to router as a test, which obviously didn't work. Rebooted the modem and router and I had 900Mbps download. Went to sleep and woke up to 30Mbps, nothing was touched on my end.
I still have 30Mbps today, whether I am direct connected or through my router. Modem is power cycled each time I switch devcies. See widermouthopen posts about the ch159 OFDM SNR values, or lack there of.
