I think PF in openbsd is still single core[1].
FreeBSD 10.x apparently has an SMP version of PF[2].
My feeling is still that if high performance is desired, FreeBSD is still preferred. For "normal" workloads though, I think OpenBSD would be a fine choice. I do like how "clean" an OpenBSD system feels.
I've not done a direct comparison but it feels solid under load. IO bound processes seem to balance IO fairly i.e. no bad neighbour problem where one process will starve another and a fork bomb won't take out the system even though I managed to hit a loadavg of 80! It still was very responsive.
Secondarily, I have a VM on BigV which seems to suffer less pauses and oddness than Ubuntu 12.04LTS did.
Works nicely on UltraSparc machines (U30 and U60 tested) as well which is a bonus. I still find them superior to Intel even if they are power hungry and rather old now. Context switch time seems pretty low on Sparcs. Not sure if it uses hardware contexts or not though - haven't looked at the code.
