[gorthaur_cruel]

"Of the others only Gandalf might be expected to master [Sauron]--being an emissary of the Powers and a creature of the same order, an immortal spirit taking a visible physical form."

If you'd quoted the entire three paragraphs, it would have been quite obvious that Tolkien was saying 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 w/o using the Ring. Here's the 3 paragraphs in full, for those not satisfied with my summary

In any case a confrontation of Frodo and Sauron would soon have taken place, if the Ring was intact. Its result was inevitable. Frodo would have been utterly overthrown: crushed to dust, or preserved in torment as a gibbering slave. Sauron would not have feared the Ring! It was his own and under his will. Even from afar he had an effect upon it, to make it work for its return to himsefl. In his actual presence none but very few of equal stature could have hoped to withhold it from him. Of "mortals" no one, not even Artagorn. In the contest with the Palantir Aragorn was the rightful owner. Also the contest took place at a distance, and in a tale which allows the incarnation of great spirits in a physical and destructivle form their power must be far greater when actually physically present. Sauron should be thought of as very terrible. The form that he took was that of a man of more than human stature, but not gigantic. In his earlier incarnation he was able to veil his power (as Gandalf did) and could appear as a commanding figure of great strength of body and supremely royal demeanour and countenance.

Of the others only Gandalf might be expected to master him - being an emissary of the Powers and a creature of the same order, an immortal spirit taking a visible physical form. In the "Mirror of Galadriel", it appears that Galadriel conceived of herself as capable of wielding the Ring and supplanting the Dark Lord. IF so, so also were the other guardians of the Three, especially Elrond. But this is another matter. It was part of the essential deceit of the Ring to fill minds with imaginations of supreme power. But this the Great had well considered and had rejected, as is seen in Elrond's words at the Council. Galadriel's rejection of the temptation was founded upon previous thought and resolve. In any case Elrond or Galadriel would have proceeded in the policy now adopted by Sauron: they would have built up an empire with great and absolutely subservient generals and armies and engines of war, until they could challenge Sauron and destroy him by force. Confrontation of Sauron alone, unaided, self to self, was not contemplated.

One can impagine the scene in which Gandalf, say, was placed in such a position. It would be a delicate balance. On one side the true allegiance of the Ring to Sauron; on the other superior strength because Sauron was not actually in possession, and perhaps also because he was weakened by long corruption and expenditure of will in dominating inferiors. If Gandalf proved the victor, the result would have been for Sauron the same as the destruction of the Ring; for him it would have been destroyed, taken from him for ever. But the Ring and all its works would have endured. It would have been the master in the end.