PS and RES are both in the same genetic family. Both have varied diets (much more than snails) but have the ability to eat /crush snails (pharyngeal teeth or crushers) . Most of your understandings are correct. The biggest differences are size and reproductive. PS can easily stunt or overpopulate if there is not enough predation. RES as best we collectively understand do not overpopulate or stunt. PS are cold tolerant where RES are not. There are several old PB articles on the question including Dave Willis South Dakota findings.