I'm guessing you're asking because you're buying them used for a really good price? Problem is if they're way too stiff, and you can't do too much with the preload (your ride height will get lower and lower as you adjust it) you're going to have to have them revalved. Now between the cost of buying them (got em used for a smoking price) and the cost of shipping them to and from and revalving charges you're into it for what you could have bought them new for. I think if this is the case you're better off waiting and buying new ones.
Damn two replies before me must have been made while I was typing, kinda answered my question......