Agree with Mickey...
Pulling the stock firmly into the shoulder is popularly believed to reduce felt recoil: definitely facilitated by a pistol-grip and hampered by a straight grip. Even shotguns designed for heavy loads, typically pidgeon-guns for example, invariably featured at least a semi-pistol grip (either 'bag-grip' or 'Prince o' Wales' grip).

The pistol-grip is for recoil control, pure and simple. A light-calibre double rifle may get away with a straight grip, a heavy hitter definitely needs a pistol-grip. The 9.3 is somewhere in between, so depends on rifle weight more than anything. Ten pounds and a straight stock may be quite OK, eight pounds and think again!