This paper reviews performance factors for comparing soft magnetic materials, including components subject to high frequency ac winding resistance effects. These concepts are extended in order to define the ranges in which they apply and provide a more direct comparison between the different ranges. The effect of permeability on component performance factors is investigated, showing that even low permeabilites can be useful for MHz level power converters. These results provide a high-level means for component designers to choose magnetic core materials and more realistic targets for magnetic materials development.