osulldj,

You're right in setting the bar pretty high for horses to be considered a "champion."
I also agree with your definition of a champion. Another point to be considered is the champion's ability to come back after injury and to run against and defeat the best of opposition, like Tulloch did.
I also agree that Sunline is the best mare I have seen, usurping my previous favourite, Emancipation. Great mares like Light Fingers, Leilani and Let's Elope are right up there but we all have our own opinion as to which is the "very best."
Good to speak to you.

Cheers.