5.2.1 stability

We've been having SMP issues with 4.9 and 4.10 on a couple different pieces
of hardware, but have had success with 5.2.1.  I asked this particular
question ons freebsd-table, but I think -current might be a better place for
it.

If we can get our necessary services running on these boxes under 5.2.1, how
stable is it likely to be?  Basically, if I setup one of these boxes as a
mailserver, and it will only ever be a mailserver, can I expect the 5.2.1
codebase to behave in the long term?

I'm just trying to make a decision, whether to limp along without SMP
under -STABLE, or chance stability but have the SMP performance.

Thanks in advance,

Adam