@rein: Gandalf was only allowed to use his power in certain circumstances and in restricted measure as he was really only in Middle-Earth as an observer/guide to those who lived there. He was restrained from his full divine-like powers because ultimately, Middle-Earth's residents, particularly men, needed to step into their greater destiny primarily on heir own strength. In the case with Saruman and the Balrog, they were both members of the same race and order that Gandalf was and as such, was able to use his power against them in combat much more freely. Truth be told, had Gandalf slipped on the One Ring, Sauron might have crapped his pants in terror as Sauron is also of the same race and order as Gandalf, Saruman, and the Balrogs.
YOU SHALL NOT PASS, Gandalf! So he wins. Lol, he would definitely destroy the Harry Potter Wizards. I have no clue who tsang jusang is. Dr. Stange is probably his toughest match, but Gandalf is over 7000, his experience is superior.