I know how fast I can get 6 aimed shots off with my 629 VS my Super Black Hawk that is why I choose the 629 for carry.
But you do understand that what is true for you may not hold true for others, correct?
The single action should not roll "in" your hand, rather your hand should roll up 'with' the sixgun. I've been a serious single action shooter for 25yrs and I've never had the need to shift my grip around between shots. If you do, you're probably doing something wrong and shouldn't be carrying a single action for defensive purposes anyway.