First 3 look good...really no argument there.
I would move Galadriel and Glorfindel into a tie at fourth...for reasoning you should look at
this thread.
Then the rest would kind of look like...
5. Tom Bombadil (Glorfindel - or someone else whom I forget - guesses that Tom would only fall if Sauron had used all of his might against him.
'First as he was last.' Pretty impressive...hmm I might even put him right behind Gandalf).
6. Saruman (Being of the same Order as Gandalf and Sauron he would probably be more powerful than most of the Elves. Now, I'm just kind of guessing this because not all Maiar - just as not all Elves, Men...etc are all equal in power. However, in
Letter 156 Tolkien writes that the old Gandalf would not have been able to deal with Saruman...so Saruman too must have been one tough cookie. Hmm now that I think about it I might put him right behind Tom B. who is right behind Gandalf).
7. Elrond
8. Elendil
9. Isildur
10. The Witch-King
That's as far as the ones you have listed. As I would throw Cirdan in there behind Elrond. Eventhough Elendil and Isildur were 'great' among Men, they were still Men and the greatest of the Elves would probably be greater than them.
The Witch-King is after all a Man...he was most likely one of the Numenorean Lords (3 of the Ringwraiths were 'great Lords of Numenor'). Sauron did enhance his powers at the Pelennor, but that just made him a Man with some cool tricks. He still operated primarily off of fear and if one did not fear him (such as Gandalf or even Frodo, Eowyn, and Merry) than he wasn't much of an opponent.
But, I think as you can see there really is no rigid, easily defined 'answers.' You can make some good arguments...and I've seen
obloquy make a good argument that Gandalf the White may have been more powerful than Sauron.