Since you'll be using this gun for home defense and personal range time with your wife, why would you want fewer rounds?

Get the seven round cylinder.

You could always load it with less, but why would you? I love my 686+ and got it because it held seven rounds.

You seem to want the 4", so get it. It clears leather easier than the 6", and it's less nose heavy. Might be handier in an emergency.

Mine is 3" and it shoots fine. Either way, you'll love it.