Really nice setup! the pfSense part made me smile!
Got anything more I can read? Dunno if I'm just blind but I couldn't find anything on this. I'd like to learn more!
We had no problem routing gigabit on an Intel Atom D525 years and years ago at a previous job. Consumer Mini-ITX board, onboard gigabit NIC, and an Intel gigabit NIC in the one expansion slot. It did require minor tuning, but nothing that couldn't be done thru the web UI.
Everything I have to manage runs plain OpenBSD managed with Ansible now, so I don't know what the current state of pfSense/OPNsense throughput is.