Not long after I made this post I tried again. This time I used the hard reset button on the back of the ASUS. I configured WAN for port 4 but plugged it into port 1 to see what happened. I got a message to connect WAN to port 4 and BAM! instant internet, straight from the ONT.
Run a speed test and got 800Mbps wired, slower than with Orcon's device.
I tried the 5ghz wifi channel and the results were similar to Orcon's device, around 300-400Mbps, though my upload was higher than I'd ever seen, over 500. Not the advertised wireless 1300Mbps + 600Mbps this Asus router can supposedly do.
My wireless adapter in my PC is fast enough, it's an Asus PCE-AC88 Dual band AC3100 with a reported 2100/1000 Mbps
Switched back to ethernet and tried again a few times, pinging the same server every time, Vocusgroup auckland. The speed has now dropped to around 400Mbps down. Not sure what's going on but I've gone back to the Orcon router and my speed has gone back to a steady 940-950Mbps/420Mbps. Guess I'll just have to live with the reduced wifi range and try dull off the LED lights.