I don't know much about "stability" and how to quantify that. I thought about the focus on security, in particular because e.g. Capsicum landed in FreeBSD and not yet in Linux, but there's a ton of security research and security hardening happening in Linux, so as an academic researcher I still prefer to work on Linux, and as an academic researcher with hopes of his work being used by real people, working on Linux is even more compelling. By the sheer size of its community and the number of people caring about it, Linux attracts a number of interesting security efforts -- SELinux came before SEBSD, ASLR hit PaX first and was then ported to OpenBSD, yama is happening on Linux, etc. So OpenBSD doesn't seem to have a huge advantage here, in terms of attracting contributors.
I would, admittedly, like to know why Capsicum was done on FreeBSD, since it seems a textbook example of cool things being done somewhere other than the monoculture kernel.
Regarding PulseAudio, I am a little sad that a hardened and stripped-down PulseAudio for servers is not obvious. I'd like to run the network server on a machine in my apartment hooked up to the living room speakers, but it brings in a ton of dependencies I'd rather not put on a server.