Firstly, thank you to everyone who has posted in this thread.
Second, I run a 1GBPS down/40MBPS up internet connection, into my Firewalla Gold Plus. This feeds my Netgear Orbi Mesh WiFi network (in AP mode). But the Nucleus Titan was served via ethernet through a few Netgear GS105E & GS108E switches with iFi power supplies. Best I can do in a rental home.
I tried the 902 first, but it offered constant drops. Then the WR1502X with the same issues, just less intense. Drops or router/AP restarts every 20-30 minutes and nothing self-recovered.
Those have been returned and I just set up the BE3600 last night. ECO mode, disabled all USB sharing, etc. Though the first two brought immediate and obvious SQ improvement, the BE3600 started off, cold, better in every area.
After a night of break-in, it's getting smoother and even more spooky 3D, but with no loss of focus. I will not be derailing this thread, but wanted to add another data point.