Not to mention network speeds even at the consumer end are slowly increasing. So having enough beef to push 1 gigabit NICs is good but planning for the future and adding 2.5 gb or higher is better. And finally having enough compute to layer fq_codel or better on top along with some monitoring all adds up.
Like a lot of projects the demand will act like a gas and fill whatever volume is given to it. Given more compute I'll find a way to use it. :-)
I'm using I5-2500K's for firewalls. 1 gigabit hardly moves the CPU usage. I have all NIC offload turned off.
Btw. I would really consider OPNsense instead if you are building custom firewalls. Pfsense is an atrocious company. Trying to kill off OPNsense by buying domains that tell lies and AFAIK no one outside Netgate can actually build from source. They are not open source even though they claim so. They are also moving to using DRM.
I've been drag racing various operating systems after my little protectli box proved only capable of pushing 500Mbit/s using PFSense + FreeBSD. Even the usual TCP tuning tricks didn't help. Meanwhile every OS I've tried except OpenBSD proved able to saturate a dedicated one gigabit link in a VM under ESXi.
I will definitely try OPNsense next!
Low power mobile chips were dual core until Q3 2017 when Kaby Lake refresh was released and brought 4 cores to the i5 and i7 line-up. Even then, entry level and mainstream versions (i3 in particular) remained dual core configs.