Well, I've got the AX89X (HW A1) in place. On the WAN side, it's connected to the multi-Gig port of a Netgear CAX80 (a combo device in bridge mode) via the router's 10Gbps RJ45 port. On the LAN side, it's connected to a 10Gbps-capable D-Link DGS-1510-28X via
this 10GTek SFP+ Twinax cable. Connecting the two devices via SFP+ using two Cisco SFP-10G-SRs and
this multimode fiber cable also worked with similar speed results.
I was pulling max ISP speeds (1200Mbps) down the WAN when I had my iPad Pro M1 connected directly to the CAX80 via
this hardwired 2.5Gbps USB-C adapter, but the AX89X's speeds are less impressive now that everything's up and running. I'm seeing more like 900Mbps down on the 2.5Gbps wired iPad Pro M1 when it's behind the AX89X. Could be that there's more overhead with 50+ connected devices.
And, of course, because the firmware on this high-end device is several versions behind for reasons I can't quite divine, I'm forced to revisit all the issues that were already solved on my AX88U. For instance, the AX89X keeps giving me DNS issues when I try to use a Pi-hole, and the logs are packed with "not mesh client, can’t update it’s ip" errors. At least one of the two AiMesh nodes, an AC88U, keeps dropping offline despite being wired—although I just watched as the other node, a wired AC68U, got disconnected for no apparent reason.
Oh, and the AX89X's GUI is slow as all get-out.
So, as always, one step forward, two steps back. I did this upgrade to squeeze a little more performance out of select wired connections, but some of my concerns about this being a "niche" device with its fair share of quirks have definitely been borne out. If anyone else is eyeing the AX89X and, like me, getting giddy about the prospect of eking next-gen speed out of their network, my advice would be to hold off for a while longer. Performance boosts are nice, but I'd rather have stability.
[UPDATE: I had to pull the AC88U as a node. It would constantly drop offline after just a few minutes. I swapped it out for a Blue Cave, which is working just fine despite still being on .384.]