Springfield P9 in .40 & .357

I've recently gotten interested in 357 Sig and I was wondering about getting a drop in barrel replacement for my P9. The guys on the Glock page gave me some good tips for the model 35. I was hoping for the same here on the P9. It looks like I might be able to get a custom barrel from Barsto. Do you know of any alternatives? What about the recoil spring; should I change it? Any other ideas or cautions that come to mind would be appreciated.