WIN from organic sources would probably last just as long as coated synthetics. Remember, N release for coated synthetics is mediated by temperature, so release is slow when its cold and faster when its hot. WIN N from organic sources is mediated by microbial activity -- essentially temperature and moisture. When moisture is not limiting, WIN releases slower when its cold and faster when its hot.
I don't think there's much difference between the two when it comes to overwintering.