Building a Router from an Old PC

I am currently building a router from an old PC I have laying around in my house. I've already bought some hardware for it (quad gigabit Intel NIC and AC Wireless Adapter). The only thing is, I don't know if the cpu is powerful enough for my connection speed (I got fiber at home). I saw the hardware requirements for PfSense and it says that you need a 2.8Ghz+ CPU if you want to do gigabit. Does that mean that I need to have a 2.8Ghz+ CPU to do gigabit wired connection between my local connections or it means that I need it to do gigabit connection from the internet. I'm confused and it makes me wonder if the 1.6Ghz dual core Pentium is going to be up to the task.

Thanks

Merci

2.8Ghz CPU is more than enough. As for the AC card, PFSense does not have support for that yet

what genneration is the 1.6Ghz pentium, I ran it on a pentium 4 and pretty sure phantom's Pentium D in the basement would be plenty too so regardless it should be fine

The CPU is an Intel Pentium E2140. As for the AC card, can I just use it in N wireless mode?