Are you interested in fire protection at all, or solely burglary protection? Also, do you plan to keep valuables in the safe other than handguns? (I ask becaus
The old battle tank you are describing sounds like a F-rate plate safe (I'm guessing it weighs more than 500 pounds). It is, from a burglary perspective, far superior to Sturdy (which itself is a very good product IMO). Sturdy uses something like 3/16 inch plates as their standard side armor thickness (far thicker than most gun safes), great boltwork, the industry golden standard 6730 UL Group 2 lock (most gun safe makers use a far inferior G2 lock), and has a solid reputation from owners. This is a good safe of reasonable pricing that basic hand tools will not be able to easily defeat. However, a F-rate (or TL-30 if built to specs & UL tested) has resistance against powered tool attacks, and most average power tools/tooling bits found in the home arent capable of defeating that safe in any practical timeframe (if at all.)
One consideration may be the lock. Many F/TL-30 safes have high-security locks. High security locks are expensive to replace in standard configurations, and on some older models they are even more expensive if the lock type or cutout is atypical, as it may no longer be produced if the Maker is defunct and a third-party lock Maker isn't currently offering direct-fit replacements. A safe expert here could better explain this, but if the lock on the older safe may need servicing and/or replacement, it is an expense you might want to factor into the price, and the safe specifics will determine whether it would be a nominal expense or something more considerate.