I know this will be long, and some parts of my post will be a little irrelevant to the whole point of this thread, but I just want to elaborate anyway.
If we are talking about individual physical power alone, Gandalf could not "kill" Sauron or Saruman (I'm putting Saruman in the argument to put better emphasis) in hand-to-hand combat (at least until Saruman's fall from his mission), nor could Sauron be killed unless the Ring was destroyed, nor could Sauron "kill" Gandalf. Sauron was only subject to death because he put much of his spirit into a physical, destructible object, The One Ring. Saruman was only subject to death because he disobeyed the rules of the Istari and fell from his status. Had Sauron, Gandalf, and Saruman dueled under normal circumstances, their physical "power" would be of no consequence, since Ainur are not bound to a physical existence.
If we define power as the ability to advance one's own goals, and keep in mind the boundaries and restraints that Gandalf, Sauron and Saruman experienced in Middle-earth at the time of the War of the Ring, then Sauron was obviously the most powerful. Because he was able to assert his will forcefully over his minions, and because he was bound by no moral or ethical guidelines, his ability to advance his own goals was greater then Saruman's or Gandalf's. Gandalf and Saruman were initially bound to the guidelines of being able to use no force over those they guided and by being unable to reveal their true power. I think it is safe to assume that the guideline for the Istari being unable to reveal true power was stringently imposed despite any attempts by the Istari to break it, since Saruman never uncloaked himself, nor did he ever assert the type of power typical of even the weakest Ainu. Because of this, even had they wanted to to, the Istari probably would not have been able to advance their purposes as powerfully as did Sauron.
The point I am trying to make is this: under normal circumstances (i.e. as uncloaked Maiar in Valinor), Gandalf, Saruman and Sauron would not have been able to "destroy" each other, so trying to quantify their "power" would be a fruitless engagement. Under the only circumstances in which they ever met (in Middle-earth in the Third Age, specifically at the War of the Ring), Sauron had more power at his fingertips, and was inherently more powerful than the Istari since he was unrestrained by rules or regulations in his efforts. I could not foresee any end to his rule without greater intervention from Valinor had he still wielded the Ring at the time of the Istari. Gandalf and Saruman may have had "potent spirits", but they could not kill Sauron, and, although they could not be killed either, they could not defeat his armies unless they revealed their true powers and took dominion over the free peoples of Middle-earth in battle, which they were inherently restrained from doing.
Going back to the original topic, Tolkien in his Letters suggested that only Gandalf might be expected to defeat Sauron if he used the One Ring. It says that Gandalf and Sauron both had an even chance of beating each other if Gandalf used the Ring. Which implies that Gandalf is no match whatsoever against Sauron without using the Ring. These three paragraphs state the point more clearly:
Possible arguments:
Tolkien, in places, indicates that things would be hopeless and Sauron would be unstoppable if he came into possession of the Ring again. My response: This would have been the ultimate defeat because the only means for overthrowing Sauron at this point in Middle-earth's history was the destruction of the One Ring. All beings with the spiritual potency to resist Sauron were either gone or leaving. Even if they (Galadriel, Elrond, and Bombadil, who doesn't seem to be interested in taking care of Middle-earth's inhabitants' business) had stayed, they would not have commanded the kind of force necessary to overthrow Sauron militarily.
Which leads into possible argument #2:
Why, then, didn't Gandalf just kick Sauron's butt? We're all familiar with the oft-discussed limitations on the Istari. These weren't limitations on their spiritual power, they were restrictions on how they could address Sauron's threat. Leading an army to destroy Sauron would have resulted in the slaughter of all involved--Sauron's armies were vast, and an army sizeable enough to overcome his would have been impossible to amass. The hope of those warring against Sauron's forces at Minas Tirith was still only in Frodo's quest. They were dead men. The limitations placed upon the Istari were actually a hint from the Powers: in effect, "you've got one hope, and it's not to put up your dukes and challenge him."
Why does Sauron need the Ring so badly, then? Obviously, to prevent anyone from seizing it and claiming it. The quote states that if someone were to bend the Ring to their will, Sauron would be broken and the effect would have been as if the Ring had been destroyed. Sauron needed it, first and foremost, to prevent this possibility (since he never conceived that someone might actually destroy it). He also wanted the power over the Three to eliminate any threat from the Elf angle.
The Ring was Sauron's anchor to the physical realm and it contained a large portion of his power. For these reasons, it was Sauron's greatest strength and only weakness, and we might cornily adjust The Don's advice thus: "Keep your friends close, but your weaknesses closer."
Remember, Sauron had been defeated before while in possession of the Ring. We might consider it a beefing item for a bearer other than Sauron (who was able to wield it) since they would have access to the majority of Sauron's power; but for Sauron, the Ring only contained his own power and was not a supplementary source for enhancing himself. This means he was merely enhanced in relation to his state while not wearing the Ring, not his original innate power.
Having said all that, here's the answer to the question.
They will become an even match. So you can take that as a No or a Yes.
it wud of been a bugger if he had taken the ring reallly
im quoting you, k?
ahhhh!!! 
