Sauron vs. Saruman

[Lord Elrond]

Many things to consider. I agree in the Silmarillion it says Eonwe was the most powerful maiar in battle. Wether or not he could overcome all of Saurons forces or not is a different matter. I also would like to point out that nowhere does it say Gandalf couldn't defeat Sauron. He was instructed to come and encourage the peoples of middle earth to fight against Sauron, The istari themselves were not supposed to do the actual fighting only counseling and supporting. They could take place in battle with others but they were not supposed to try to go one on one with the Dark Lord. Sauron s actual physic is not stated after he was destroyed by Isildur, Gollum states that he has four fingers on his hand but he is also described as being an eye. These I think are metaphors or could be at least. I dont' think Sauron is actually as he was portrayed in the movie but neither do I think that he was in quite in human form either.
I do agree that Sauruman could never have become a super power on his own. He would have to keep the ring to be that powerful and by keeping the ring Sauron would still be in control because his fate is bound to the ring. Without the ring he is still just flesh that can be destroyed as happened by wormtongues hands and possibly happened to the blue wizards