Archer C7 v2 Wifi upload vs download cirq/speed difference


I run overclocked C7 v2 as "dumb AP" with everything maxed (80MHz 5GHz). I noticed that WiFi speed is lower when downloading (99% sirq) than uploading.
Basically, download runs out of sirq around (true iperf3) 450Mbit where upload will hit 600Mbit/sec and more (again, measured by iperf3).

And yes, I am not running iperf3 server in the router itself but on separate wired x86 PC. And iperf3 client is been run on different WiFi clients but downloads are always slower.

I am using non-ct "ath10k-board-qca988x" driver and ath9 is disabled/not loaded. firewall and dnsmasq are disabled.