Ok a 12% differential on a LAN is kind of surprising. I wonder what Tailscale could possibly doing that would be causing this issue because aside from the control plane I don't believe they're in the data path all that much. Maybe WireGuard on Windows isn't as optimized as it is on Linux?
IME it adds about (at least) 1ms of latency over local networks. You should be able to use a different dns suffix to use the LAN interface instead of Tailscale.
These are on my local network, connected to my switch over 1gig Ethernet.