As far as passing packets, the two are comparable. Our web interface will be a bit slower on hardware of that spec, just a lot more things going on, we have protections from attacks against the web interface that m0n0wall doesn't have, amongst other differences. If you have a busy dashboard, it'll really hammer a box that slow, especially if you show the traffic graphs on the dashboard. Everything else is much less difference. Unless it's something you're constantly in making changes, it wouldn't be a big enough difference for that to be a factor.