What are you going to do with them after they're in the ground. If I were building a fence, I would peel them and give them several coats of Termin8H20. I would especially fill some shallow pans with the stuff and stand the posts in them (tilted against a wall) so the posts can absorb the stuff up the end grain. I'd let each post soak for 2 days on EACH end (you'll need to keep adding more preservative). If you plant untreated posts in the ground, water is going to wick straight up the center and rot them out in just a handful of years. The chemical will not prevent the wicking, but it will greatly impede decomposing organisms from rotting the wood.
If all you want to do is stick posts in the ground at the end of a road (not building a fence) as a road block, and can easily stick in more in 5 years when these are rotten, then I wouldn't bother with the preservative. If you're investing all the time, effort, and money for a fence, however, you might want to put some $ into making sure it lasts for awhile.