Where Does Zenyatta Rank?

Where does Zenyatta rank among the all-time great race horses? Take a look at the Bloodhorse list of top 100 U.S. Racehorses of the 20th Century. Where would you put her on that list? I'm comfortable putting her as high as #21, right between Swaps and Equipoise. I just can't justify any higher than that...not enough fast times and wins by wide margins. Maybe if she had the benefit of running more races on dirt that wouldn't be the case, but unfortunately that wasn't the case.