i disagree a little.
Yesterday i also tested iperf3 and got 900/900 mbps IPoE with 1.7% load of cpu.
Laptop (debian+marwell) 192.168.x.x as a client<- 1Gbps -> lan-Mi3G-wan <- 1Gbps -> desktop (windows+realtek) 10.10.x.x as a server.
May be i am doing something wrong, but 900 mbps
OpenWrt SNAPSHOT r15635-799fca7602 / LuCI Master git-21.020.56896-af422b1