I'm sorry, but this just isn't the case, alcohol has a set amount of energy per gram. If the same amount of fuel were used to heat an aluminum skillet and a cast iron one, the cast iron one would only be a fraction of the temperature of the aluminum one. Quite honestly though, the thermal mass of a cast iron skillet, the very thing that makes it great to cook with, is also the thing that makes it difficult to use on a camping stove with limited fuel.

I'm actually not even sold on cast iron for home use. It's heavy and awkward on a stove, and not as non-stick as non-stick. A good clad skillet has a better thermal mass (Cast iron per gram is fairly low, it's only in sheer mass that makes it so good), and a good teflon coating is better than even the cast iron skillet you inherited from your grandmother (at least in my experience), and you can cook acidic foods without worry.