Wireguard speed

[Роман Строганов]

Help with speed in the wireguard vpn.
There are 2 routers linksys with openwrt 19.07.7. And the wireguard 
tunnel between them.
If the link between the Wan of both routers is 1 gigabit/s, then the 
speed inside the tunnel is 300-370 Mb/s, which I think is good. I 
understand that these are simple routers, not servers.
This is done for the test.
In real life, the speed between the feasts will be limited to 100 Mb/s.
I decided to do a test and lowered the speed on the switch ports 
(routers connected through a gigabit switch) to 100 Mb/s. After that, 
the speed between routers through wg is 30-40 Mb/s. Processors on 
routers are loaded at 25-25%. Once I am on a channel in 100 Mb/s. 
received speeds between routers 85-90 Mb/s. So such speeds are possible 
on the wireguard.

After that, something went wrong with the electricity and the routers 
were rebooted. I didn't have time to save the settings.

 From memory, I set everything up again, but now I can't achieve high 
speeds...
I measure iperf3 installed on the routers themselves.

How can I get ~ 80-90 Mb/s again via 100 Mb/s channel?
I will be grateful for any help in setting the speed wireguard

p.s Forgive my English. I do not know him well and use a translator