Could Gandalf beat Sauron challenged one on one?

[Armetiel]

defeat Sauron as in throw him down for awhile or destry him completely...because as long as the ring was in existance the latter could not be done...However, in the case of the former it is my opinion that Gandalf could take Sauron one on one as you say. I mean, if you really think about it, ALthough it wasn't really one on one, it kind of almost comes down to that when Isildur defeated Sauron the first time. And Sauron HAD the ring then (well other than the fact that Isildur cut it off) but he was a huge power at that time too. So especially without the ring, I believe Gandalf would be the stronger.