In the AP config … Fairly complex queue handling, bridge filter, IP filter addition, packet marking … I hope the AP processing power is not the bottleneck.
Setting priority does things internally, also for wifi WMM priority, but be aware of the lack of “AMPDU enabled” setting in MT by default for other priorities than priority “0”,
No AMPDU aggregation for priorities 1 till 7 , if used, will waste a lot of air-time for everyone in the channel and drastically reduce wifi throughput.
I don’t know if all those queue throttlings to the WLAN interfaces could not even break AMSDU aggregation by delaying IP packets, what would be a wifi throughput disaster.
http://forum.mikrotik.com/t/help-mikrotik-capsman-wireless-download-speed-max-200mb-but-pcs-mobiles-link-speed-is-866mbps/142677/1 , http://forum.mikrotik.com/t/help-mikrotik-capsman-wireless-download-speed-max-200mb-but-pcs-mobiles-link-speed-is-866mbps/142677/1
Removing 6Mbps basic rate can be good tuning, if needed. Otherwise it causes more disconnects and disables weak client associations.
(One AP/SSID at 6Mbps takes only 0.5% of available air-time in the channel. The old 1Mbps basic rate for 802.11b was 3% air-time, and that was often exhausted then with 30 AP/SSID)