I dunno if this is entirely true- my current pfSense router gets as close to line speed as I'll ever be able to get with my setup (~900 both ways to a test server in Chicago and on LAN) and I'm running an (overkill) i5 in my generic Chinese minipc. It's possible that I don't have Intel NICs but I swear I do

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!

[citation needed]

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.

Mine certainly can