You all seem to be implying that they will even read your letters. I can't tell you how many times I walked in there and they had not even looked at my file. I would go with the big-wig b/c at times the most attention your file will receive is them flipping through your CAS file, looking at who wrote your letters, and assuming they are good. Be realistic, how much attention would you physically be able to give each application if you had clinic, teaching and research responsibilities on top of having to interview applicants? Sorry to say it, but the world is a bit of a good ole boys club, and it helps to have someone write a letter who is a member of the club. Regarding private letters, have them mail the letters directly to the program where they did their residency. This will provide name recognition at that institution that might not be available nationally to separate you from other applicants. They might be a member of "the club" at their home program, whereas they would not be on a national scene.