pci is a shared bus with a max of 2 gigabits. you'll see a gigabit but never see two or more.
I am aware of that. But as I said it depends on your particular needs in *concurrent* traffic. Although it cannot sustain simultaneous Gigabit debits on all interfaces, i can sustain Gigabit bursts that are not simultaneous, as is often the case.
I have found that such a solution is perfectly capable when isolating a LAN, or several LANs, from a WAN, for example.
If you really need concurrent Gigabit traffic on several interfaces, I would suggest that you get proper *dedicated* firewall/router hardware instead of building one from standard parts. It will be much more efficient.