PS do well up north but they are not a true substitute for RES. Several of us have looked and we find no evidence of any reported cases of RES overpopulating and stunting. That is just the opposite of PS who regularly overpopulate and stunt. They do both eat snails and are beautiful fish. If bigger panfish are your goal then PS would not be a good choice to add to a northern LMB/BG pond IMO.