Spreadyawings: That surgeon question is the bomb!, I’ve been asking myself the same question, but I have a few years to make up my mind.
There are number of ways to thin the list and when you use them all together it can really help narrow things down. "Do you want to be a surgeon?" is one; "Do you want to work with your hands and how comfortable are you with not knowing the answer?" is another. The newest one I am using is the depth of knowledge approach. "Do I see my future practice as a wide or a tall rectangle along the spectrum of knowledge?"