Read a little bit on the BuffaloBore page regarding 38 Spl & .357 Mag in revolvers. It's quite decent information and "real world" with no B.S.
BuffaloBore Product Line Listing
Get the .357!! I had a S&W 442 (.38 sp+p) was a good gun, sold it, bought a S&W 340M&P. Love this gun! It is tough on the hand when firing, but I am sure I will not notice that in a real defensive situation.
If you like the .357 and the J frame 5 shot, consider the S&W 640, it's identical to the 642 only it's all stainless steel. the advantage is better weight to manage felt recoil along with the ability to finish the revolver with bead blasting if you ever want to. The clearcote finish on the 642 will be the first thing to show wear and you can do anything to refinish it other than to send it back to S&W.
Now if you buy a 640 you can send it to Gemini Customs for a trigger job and it'll improve it's shootability a 100%. You can practice all day long with light .38 wad cutters and carry either .38 +p's or .357's. I'm not sure how the weight will be in the pocket though. It'll definitely be heavier than the airweight but it'll be a better shooter.
Just a thought. I'd personally like to have one of these although I only have the 642.