To see others' unpublished posts, "Bypass content access...
Book element
"Bypass content access control" really means let users in a role with that permission view unpublished content (and edit and delete any content, unfortunately). Administer content does not grant this power to see unpublished content nor to edit and delete any content. In Drupal 7 this permission seems to do little more than what the separate "Access the content overview" page does.