Do not compare Barbaro to Seattle Slew. While Barbaro has twice taken down horses who were 5 lengths better than him on paper it still remains to be seen if he can win the TC.
Seattle Slew was the very best eye to eye intimidator in racing history. So thought Angel Codero Jr. who rode on him and against him.
Seattle Slew knocked out the great Affirmed by 18 lengths (1978 JCGC) with eye to eye pressure and put away Cormorant (Gotham Aqueduct track record holder) in the 1977 Preakness in the fastest mile ever in Preakness history.