I'm using rt-ac67u twin pack, in a full wireless setup, on a 5000 sqft bungalow house with unifi 500mbps. I want to upgrade to a new router and keep these 2 units as nodes, still in a wireless setup. I don't know is AX92U , AX3000 or AX82U a better choice? Especially, considering the compatibility issue of Wi-Fi 6 router pairing with WiFi 5 node.

Can someone help explain the pro and con of these 3 models as the router?

Let me clarify.. .

I'm using rt-ac67u twin pack, in a full wireless setup, on a 5000 sqft bungalow house with unifi 500mbps. I want to upgrade to a new router and keep these 2 units as nodes, still in a wireless setup.I placed router on ground floor, connected to TV box via Ethernet. On same floor, I have the node in a bedroom 10m away, it is connect to the box via Ethernet as well.

Intending to keep one ac67u as node on second floor, I don't know which WiFi 6 model to choose? Is AX56U, AX92U , AX3000 or AX82U a better choice? Especially, considering the compatibility issue of Wi-Fi 6 router pairing with WiFi 5 node.

Can someone help explain the pro and con of these 4 models as the router?

I only intend to buy one unit of Asus Wifi 6 router now.

Assuming I take dual band TUF5400 which has wider coverage.
My 2 unsolved questions.
Can I set it's Wi-Fi 2.4Ghz ONLY to compatibility mode to connect with my existing AC67u as node? Aim for the node to maintain WiFi speed...
AND at same time, keep its 5Ghz band in Wifi 6 mode? Aim to exploit the higher speed.

If I take triband Ax92U Instead, what difference to these two questions?

I have a TUF 5400 as Main and intend to add a WiFi 6 router to be connected with Cat 6 cable, to be place d on second floor of my bungalow. It will be some 25m away cable length apart. There will be two units of AC68U as wireless node. Which Wi-Fi 6 Asus model will you recommend?