The traditional wing loading based on weight/wing area is good when comparing models of roughly the same size. The oz/sq.in. numbers we are used to see is mostly good for planes in the .40-.60 size. When you get into 1/4 scale and up, higher oz/sq.in. will actually fly similarly to lower numbers for smaller planes. I've seen suggestion of "cubic loading" to be used instead of the conventional "square loading" when comparing models of varying sizes. Seems to work fairly well.