Xtreme has different finish, xtreme double action trigger installed with trigger work done. I think that's it, I've never personally owned one. Regular model with trigger job will blow the xtreme away. S2 has cone barrel, hard chrome. S3 about quarter inch longer, about 3 oz heavier or so, all weight in the front, less durable finish. I'm sure there are other details I'm forgetting at the moment.