I would have to say 6 " would be the ideal length, even though my 686 and 629 are both in 8 3/8" and my Bisleys are 7 1/2". I have fired 629's in 6" and found them to be very controllable. Feel the six inchers are still not too big for home defence, probably a bit much for CCW, but excellent for hunting purposes.
Have to admit though, when plinking at the range with full house loads for my 8 3/8" 629, I barely notice any recoil (perceived or otherwise). It makes sighting for accuracy a real possibility for a guy like me who doesn't enjoy heavy recoiling guns. Safe shooting.