The whole bit about the breaking of Saruman's staff, as well as his comment about Gandalf wanting the rods of the 5 wizards, and Wormtongue's orders about the staff all indicate that a wizard's staff is not just a piece of wood.As far as that goes, Gandalf was more than a match for any one of the nazghul, perhaps een all of them. He was a Maia after all. In fact, he was pretty close to Sauron's equal, although perhaps less of a warrior and more of a counsellor.
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