To me, the Bisley / SAA grip choice is an identical puzzle to that of the 1911 - 1911-A1 flat/arched mainspring housing.
It's not just a size and reach issue, but one of grip angle. To me, Bisley's and 1911's naturally point low, while Peacemakers and 1911-A1's are just about perfect. The short version is you won't have your answer until you wrap your fist around both.