spitfires are a good head, but I don' t think they are suitable for your setup. Pulling only 50lbs you Kinetic energy level just won' t be high enough to get reliable preformance under reasonable conditions I personaly feel you will be much better off with a good fixed blade head or as ausieguy said, a good cut on contact style head. Magnus stingers would be an excellent choice as would a muzzy 3 blade or wasp sst, golden key deadheads, or thunderheads would all work well for you provided your bow is tuned properly.