What kind of suppressor are you going to use?
Don't forget about .45 Colt and .44 mag./spl. calibers. Much more foot pounds of energy and still subsonic (less than 1000 fps.+/-). I think the lever action would be a great suppressor host. What about the Rossi "pistol" carbine? Can't think of the name of it right now. You could always shorten the mag tube a little if necessary.
I'd prefer to stay with a 357 because I can run 38 special, which is a really cheap round to shoot. Also, I would prefer to stay with a .357/.38 so I can get a revolver later on in .357.