Fella's;
There's some huge problems with trusting just a set of numbers provided to you by the manufacturer of an RSC. If you don't know what the test procedures were, you don't have enough information to make good decisions between brands, or if any brand provides enough protection for you. Go to the Underwriter's Laboratory website & find the specs for their one-hour thermal protection test. It's incredibly detailed, but when they say it passed their 1750 f for one hour, holding the interior temperature below 350 f test, you can be sure it's true data.
I've posted on this several times in the past on this site, but I'll go ahead & do it again. Thermal protection isn't rocket science, the methodology of how to provide it has been known for hundreds of years. Simply put, if you have more, or denser, or both, materials between the heat source and what you want to save, you get better protection.
Sheet rock is a good flame barrier, but it's not dense enough to provide a substantial time delay to heat soak. Sheet metal is just that, a thin layer of a dense material; emphasis on thin. Therefore, any RSC has to stack several layers of gypsum wall board to get a better true insulating capacity. Which takes room out of the interior of the unit you just paid some pretty good money for. Yes, there are now units that use a foam insulator that's supposed to be superior to sheet rock. They are high refractory/low density "plastics" that work kinda like this: They have a high melt temp for the plastic that gives a stable wall for the air bubbles that are actually the insulating medium. And lots of air bubbles mean low density/light weight.
Not being in the testing business myself, I don't know if they actually give the RSC a marginally better thermal performance factor, or a superior one. I'm old school, and I know that solid steel plate and concrete do have the ability to pass the U.L. one-hour test. Up the thickness of the steel plate & that type of construction will also pass the U.L. two-hour test.
True safes, not RSC's, cost more because they use better materials and more of 'em. Whether or not it's worth it to you is a personal decision you have to make. But, if the worth of your valuables is at least that of a true safe, how much can you afford to lose? Which, I admit, begs the question of how much does a true U.L. rated safe cost?
I sell Graffunder safes, and I'd be glad to quote you via PM if you so desire.
900F