The 8 gauge side by sides where a thing of the past and more around the time of BP loads and punt guns centuries back.
Hence hunted with one in my youth during a fox hunt, and with the amount of smoke produced, and recoil as well, can not phantom touching one off with a smokeless power full loads of today strength while sitting in a boat goose hunting instead.
As for the slag guns, have fires both the 8 gauge and the 4 gauge versions, and no way in hell that I would every dream of such in a 4 gauge SXS shoulder fired instead. Hell, half few shots in with a SXS 8 gauge even standing with the current slag loads, and trip to do the doctor would be in order to reset your should back in the socket.
Truth is, now in my longer tooth years, still shot a 10 gauge, but it's a semi auto to suck up a lot of the recoil; with the old 10 Gauge side by sides left as wall hangers display pieces isntead.