The newer XDm has a 3.8" barrel that holds 16+1 in .40 and one in 9mm that holds 19+1. The slide has been redesigned so it is more like a "A" shape and also the serrations are different. I've been looking into the 9mm model. And now they have a compact model that has a flush fitting mag that holds 13+1 and a extended mag for holding 19 in the 9mm and a 11+1 mag and a extended 16+1 in .40.
As far as the .380 round I was reading a interesting article in S.W.A.T. Magazine titled "Don't bet your life on the .380." It is by someone who has been a federal firearms instructor for 25 years and of all the things in the article that stuck out the most was that he said the .380 round has only 80% of the speed and energy compared to a 9mm round. I'll bring it home from work and look up some of the other things that were relevant to the .380 vs. other calibers.