How About A Firebox Capacity and Dimensions Database?

Unless I had a lab and LOTS of clear documentation, I would not want to hazard such guesses!
Many stoves even accept some 16" logs and then some 20". It would be very hard to get an idea of exactly how they compare. You COULD get such a comparison if you had the same pile of the same species of wood (some have more twists and knots) and then loaded up each of the stoves when cold.

We did that in our shop with various stoves and found, for instance, that you could get a lot more wood in an Intrepid than in the Jotul #3.

But, realistically, this often has gotten reported here by users anyway - or in the stove reviews.

I classify this as a good idea - but not one that I can do....