Cool. Final numbers:
Not 250-capped, but egress out of .141 looks shaped at ~480 Mbps. iperf3 server
stopped, iperf3 left installed on both boxes (handy for next time).
j@dev:~/code/public/dropshell$ cat ~/.config/magicssh.env
# MagicSSH configuration
# Edit these values to match your relay server setup.
MAGICSSH_REGISTRY_URLS="http://45.38.149.240:8199"
MAGIC_REGISTRY_TOKEN="weorjfhnbbivdjf9uy34823necn12124vnb"
MAGICSSH_RELAY_HOSTS="45.38.149.240,51.161.208.141"