I got a great letter from a very well-respected PhD Ortho basic science researcher, and I know that it helped on my apps. Everyone has good clinical letters, and you will too. Yet, every time I go to an interview, the one that they want to talk about is the research letter. I used my letter, and milked it for all it was worth, and I'm completely convinced it got me interviews at some great programs that wouldn't be interested in me without it.