[Boromir88]

Intimations are made that Gandalf, though not head of the order or council, was the greater of the two, but I would call these tenuous and certainly a strong case can be made to the contrary.

I don't know about that. Saruman the White was certainly more powerful than Gandalf the Grey (but was Curumo more powerful than Olorin?), because Saruman was placed as the head of the Istari. And as the head, he was granted more power, or the ability to use more of his power.

In dire needs Gandalf would reveal his true power (for example his fight with Durin's Bane), but he still remained in conformity to the Rules that were placed upon him, where Saruman didn't. Saruman the White was more powerful than Gandalf the Grey, but this was only because of the restrictions placed upon him, and his over-whelmingly good nature of following these restrictions:

This is sort of a nifty what if scenario that Tolkien gives us. Where Gandalf could give Sauron a run for his money.

One can imagine 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.~Letter 246

And Saruman was a great studier of Ring-lore, but I think we can question exactly how much he knew...considering the Ring he attempted to make seems to have been a failure and he hadn't worked out all the kinks yet. And finally, it takes more than knowledge to master the Ring:

If that would happen, the new posessor could (if sufficiently strong and heroic enough by nature) challenge Sauron, become master of all that he had learned or done since the making of the One Ring, and so overthrow him and usurp his place.~Letter to Milton Waldman

Which brings up the questions
1. Did Saruman have the necessary strength? This I admit can be debated. Because I do now see a bit of ambiguity with Letter 246. 'only Gandalf might be expected...' So even though if Gandalf is the only one 'expected' to challenge Sauron one-on-one, it doesn't necessarily mean he was the only one capable of doing so.

It's like if I said, I only expect Italy to beat USA. It doesn't mean that Italy would beat them, or is the only one capable, but it's the only team I 'expect' to do so.

2. Did he have the knowledge that it took? Saruman went into studying Ring-lore, but was this the right place he needed to actually master the Ring? As this quote suggests you need to look more at Sauron and what he was doing after making the Ring, than the Ring itself. And this is something we know that Gandalf did do (and the reason the Istari were sent to Middle-earth), as we find out he alone goes through Dol Guldur and to find out about the 'Necromancer.'