Ah! Can I ask you what you get for wired speeds through the ethernet port on your bridged AC? In other words, what do you get connected via ethernet on the router not connected directly to your ISP?
I'm thinking of replacing my AC with something like the Amplifi HD, but maybe I should just buy a second old Extreme AC?
I don't have a really good way to test, actually. At the moment, I don't have a network-attached SSD (my NAS is all spinning HDDs) to do a good test with. Testing with spinning HDDs won't be useful. However, via my Mac and/or PCs connected via ethernet, get internet speeds of 940+ Mbit/sec (I currently have 1.2Gbit service to the house), all without appearing to disrupt other internal network traffic (Sonos, 5 continuous-stream Nest cameras, etc.). So I know that the gigabit ethernet network in the house can carry pretty close to practical data speed limits; thus the Airports' gigabit ethernet ports don't seem to be a significant bottleneck.
Now, while it may seem useless to have 1.2Gbit (theoretical peak) to the house when the network inside the house is limited to 1.0Gbit (theoretical peak), the cable modem conveniently has 4 ethernet ports. One is connected to my main gigabit switch for virtually everything in the house, and another connects directly to the Cisco Meraki hardware VPN device I need for my work PC, dividing it into two separate network segments. The VPN is provisioned for about 300Mbit/sec (max. I can get from work), so I'm able to get essentially full performance service out of my hardware work VPN, plus gigabit service for the rest of the house without one impacting the other. Works out great. And I've seen 900+ Mbit/sec speeds from the general house network while still getting around 300Mbit/sec off the VPN simultaneously (later at night, of course, when the rest of the neighborhood cable service isn't saturated, too).
