I bought a new PS3, and it was on 3.55. As far as buying it new, the PS3 systems are sold in the stores within one week from ordering. (accroding to Gamestop, Best Buy, Wal-mart) They said they're shipped with the latest 'stuff' on it, as far they know. They couldn't tell me. So yeah. Sadly, the only way to know 100% sure is to go to GameStop or something like that, ask them for their OLDEST PRE-OWNED system they have in stock, and go from there. I did, and I ****ed around with the guys who worked there, and convinced them to open it up, and plug it in to see what firmware it was on.
Be cool, don't be gay, and they'll pop it open to check it out for you, I'm sure, giving they're not busy.