OpenBSD has been my go to firewall since my firewall was a Sparcstation IPC. There have been some major changes along the way, but most of the time rebuilding the system takes less than an hour and is a matter of porting a few config files to a fresh copy of the OS. Even the major changes are usually trivial since the documentation is kept up-to-date and there are plenty of examples in the docs and on the mailing lists.

The last time I saw anyone test packet passing speeds against OpenBSD it was around the time of the pf/ipf split and rewrite and OpenBSD was the slowest of the lot. Although modern hardware can saturate a cable modem, the multithreading of their network stack is still a positive, as is the work to support modern wifi cards (N); hopefully AC will be next.

Also definitely looking forward to pledge since it further reduces attack surfaces on an already hardened OS.