Interesting, I can get around the same wifi speeds as you in iperf3 but only on stock firmware. On Openwrt, they drop by about half.

With Cat6 wired LAN, I get around 900 with both firmware versions, which would seem to suggest that my problem is specifically with wifi. It could be that with the IPQ4028 radio you can’t realistically achieve more than 250-300 but what is still annoying is that I can’t even get that with OpenWrt, whereas you apparently can! What a mess…