Look at the Match top 3 or nah thread (I dont know how to link, but from 1/4) I replied there and pasted relevant charts from NRMP data there. It was way lower last year than most people think. Basically if you rank 5 or more places you are pretty well set.
That said, it isnt that expensive to do a few extra interviews which provides some security and may show you a program that unexpectedly is one which fits you well.