The Making of a Router

Hello Everyone, We are looking to put together a 2u server with a few PCIe 3 x8 (recommendations appreciated). The router will take a voip transcoding line card, and will act as an edge router for a telecom company. For things like BGP (Quagga, Zebra, all that lovely stuff!!!), static routes, and firewall capabilities we are thinking gentoo linux stripped for sure however, what about the BSDs? FreeBSD or OpenBSD. Any comments, feedback, does, and don'ts are much appreciated. Kind Regards, Nick.