The audition rotation will help you for that school, but a great step 2 score will help at all the other schools. An "honors" grade at an ortho rotation at X school won't differentiate you from everyone else, because pretty much everyone gets honors on ortho and everyone gets letters of recs that say they are the best thing since sliced bread. So, having 4 ortho rotations vs 3, or 3 vs. 2, doesn't seem that huge of a deal in my opinion.