[Gurthang]

Obviously, Gandalf was limited in his ability due to his 'Istari' status. Not that wizards are weak, but he was comfined in a human form. This would make him considerably less potent.

As far as the rings are concerned, Sauron created the One, which was specifically designed to dominate and control the others, so I doubt Narya would have assisted Gandalf much against the Dark Lord.

But on the other hand Sauron was somewhat weakened without his ring, so Gandalf would have that advantage.

In the end, I would say Sauron would come out on top. But I'd still cheer for Gandalf!