What's wrong with FreeBSD 4.11? You said it's stable for you. OpenBSD is going to be a big change for you on short notice with little testing. Everyone says the 4.x branch is much more stable than the 5.x branch anyway.
It is, but its unsupported. If I go back to 4.11, within 6 months I would have to go back to 5.x anyway. I'd rather not waste time doing that.