Uhhhm, I don't know for sure, but I don't think period RenFaires usually use PA at all, it's usually up close and personal. But you are right, there are other places that use them and it is important. Do you have your own sound, or are you relying on the venue to provide it? If you are relying on venue, it is doubly important to check it!
I am sure when MMario gets back he will have specific suggestions for RenFaires.