Priest and Maiden are pure heavy metal, not really power metal. Power metal, as a genre, usually includes mostly double bass driven songs with fantasy lyrics, usually reinforced with high pitched vocals. Although Priest and Maiden certainly have covered that ground, they typically write about things other than unicorns and dragons, and rarely use double bass rhythms. I would say that for consistency and staying true to style in power metal exclusively, Gamma Ray, Helloween, Edguy, Strato, and Angra are at the top of the heap, really.