I have carried a DW in the past, I am curently using a S&W 19 on and off. I like the .357.
Why step down to the .38? You have a nice medium frame revolver that should be relitivly pleasent to shoot with a standard .357 loading.
Why use less?
Using .38 loads will change the way the gun performs a bit. I would reccomend finding a single load for the gun that you like. Use it as your primary and as your speed load as well. Consistancy is good.
I like the Winchester 140gr Silver Tip in a 2 - 3" as it seems to flash less in low light and Federal 158 jhp in 4-6", this is strictly a personal preferance.