If it HAS to be 4" and no shorter, then I'd say yes look for the 4" SP101...I love my 2" version. If you can do a 3 or 2" barrel, it be much easier to conceal. That or one of the Service/Security 6 models.
There's also a smaller version of the S&W 686 with that sizing...the model number escapes me.
Either way, .357 is the way to go, as you have the option of what caliber to shoot.