I'll give you a horse that may not be quite as accomplished as Ferdinand or Alysheba but when he ran his best, I think Lemhi Gold would have easily beaten either of those horses. He did win Champion Older Horse in 1982.
Lemhi Gold was an absolute freak when he fired. For those of you that have never seen him run, here is a replay of his win in the Grade I Marlboro Cup at Belmont:
http://www.youtube.com/watch?v=ovmxhqF-TJk