I'm running an HAPax2 as my main wifi AP which supports 5Ghz-ax and uses the full channel range, and have an Audience running as a WiFi extender. The Audience doesn't support 5Ghz-ax and it splits the 5ghz-ac and only uses half the channels as ap on the 2nd radio and the other half as station-bridge on the 3rd radio. So HAPax2 should perform better.
My Android using speedtest.net can get 620/550 Mbit down/up on the HAPax2 and 440/440 on the Audience as you would expect.
The iPhone is getting 230/200 on the HAPax2 but gets 500/500 on the Audience - what's going on there?
Both HAPax2 and Audience are running routerOS 7.12.1 with wave2 and capsman