WG is quite fast. Can’t be the limiter. Like this guy I’ve driven 1 G easily on 7950 and Epyc 9654. I think I did 10 G but I can’t recall because at some point I just moved everything local and did 40 G. But I’m sure it would work on CPU on reasonable machine
A very likely culprit is the packet encapsulation changing things for the worse. An informative test would be to tcpdump (wireshark, etc) the packet stream with and without tailscale. Look at packet sizes, etc.
The overhead shouldn't be 15% but there could be some weird interaction with the link MTU for the VPN causing, e.g., smaller packets to be sent with more overhead.
https://old.reddit.com/r/mikrotik/comments/112mo4v/is_there_...