Alot of people have wondered about this. It's not posted anywhere and if it were it wouldn't be a very meaningful stat. I'm sure Harvard has a high avg Step1 but I'd imagine that has more to do with the quality of applicant they admit rather than their groud-breaking pathology cirriculum.
My school prided itself on a long series of "boards review" lectures in which the PhDs who have no idea what is on the test came back and repeated their favorite lectures about patterns of viral genetic replication. It was completely useless. At the end of the day, Step1 comes down to you, your desk, your copy of FirstAid, and a looooong 4-6 weeks.
Good luck to you.