Expected speeds?

Hi there
I’m just testing Tailscale with the following setup:
Ubuntu 22.04LTS on subnet A
Windows 2019 on subnet B
Both subnet A and B have 1Gb internet access, which has been tested via speedtest to be close to 1Gb up and down.
Yet when testing iperf3 between the two system we get about 128Mb with 4 parallel streams.
Where none of the systems are anywhere close to 100% on their CPUs.
We have of cause checked that both systems are connected directly with “tailgate status” checked that UDP is enabled and MappingVariesByDestIP is disabled via netcheck on both systems…

So why are we not getting better performance between the two systems?
We have an existing IPSec VPN where we can reach about 400Mb… we of cause hoped that tailgate and wireguard would result in better performance than IPSec ?

Is there anything we have missed or something we can test?