Rondog;
That's an excellent reason to very carefully research, if you can, the differences in the thermal protection ratings amongst the RSC's in the market today. However, finding the details of the testing methods & differences between the Omega Laboratories, Pyro-3000, BTU, and other cited thermal ratings is nigh unto impossible.
In my professional opinion, the only one worth paying any attention to is the U.L. one hour test. With that one you can go online & find out how that's conducted. With the others, well, was the safe upright in the furnace or laid on it's back? Did the test period timer start when the interior of the furnace reached test temperature, or when the gas was lit? If when the gas was lit, how long did it take to ramp up to the rated test temperature? In other words, did it spend eight minutes out of 30 at 1200 degrees, or 25? There are at least a dozen other questions like these that can be posed, where the answers make a material difference in the actual protective capabilities of the unit you may be considering buying.
Good Luck, 900F