The 5200 is listed at 80000. The king is about 48000
To be accurate, they were not tested using the same method. Also, the 80k you mention is in-house calculas. Our in-house calculus numbers are closer to 60k. Neither is comparable, because tremendous assumptions are being made.
Method 28R, which will become popular again after EPA's announcement in the Federal Register tomorrow (EPA has withdrawn the cordwood method due to serious concerns) uses dimensional lumber. The test is over when the scale reads zero, meaning all the test fuel has been consumed.
The cordwood method tests are deemed over when 80% of the fuel load is consumed.
The "as tested Btu's" are based upon the above.
So, if you put 200,000 Btu's into a stove and burn it in 4 hours, and tested using the now no-longer available cordwood method, you get 50,000 Btu's/hour.
In the second stove, you put in 200,000 Btu's and burn it in 8 hours, on the crib method, you get 25,000 Btu's.
See, you can't compare numbers from brochures or stoves tested to two different methods.
What you can do is say what your personal experience has been, which you have done so.
My personal experience is mine. My King heats 2,850 square feet better than 2 other stoves from other manufacturers that were nearly as big that we used prior to my King's.
EPA has acknowledged they are disturbed how some companies have used buoyed figures to laud-over other manufacturers numbers. The FRM (Federal Reference Method) is a few years out....but will hopefully address these deficiencies.