Dedicated thieves with enough time, I think can overcome any kind of safe or secured room.
If you locate your safe on the main or second floor then a reciprocating saw will free the safe from the building and the thieves can just drive off with the booty. If you cement your safe in the basement with screws and lag bolts in cement and concrete walls the thieves can just use a jack hammer and in a matter of minutes can compromise your best efforts. Even if they cannot free the safe, an acetylene torch will do short work of any safe you buy.
I think the only reason to have a safe is to prove to the judge that you are a responsible gun owner. It has nothing to do with protecting your firearms from theft. In fact I think a safe is a magnet for thieves. They now know where the valuables are and find it an interesting challenge to break into the safe.
You've convinced me. I think I'll throw all of my guns out in the yard, so nobody's tempted to try and steal them.