[jimpudar]

Correct me if I'm wrong - I haven't tried it - but it looks like you should be able to run OpenBSD on ARM https://www.openbsd.org/armv7.html

I'll check what the energy consumption on my router is. I'm using an AMD chip which I had lying around. You're probably right that it uses a bit more power than necessary.

I was thinking about getting something like this: https://www.amazon.com/Firewall-Micro-Appliance-Gigabit-Bare... which uses 10W. It should be easy to install *BSD on something similar.