I use IC/M in a straight stock SxS for upland hunting and works great on francolin and guineas with 34gr #5. I’ve tried it on pigeons, however prefer tighter chokes. I use M/IM for pigeons and waterfowl with great results (gyppos, ducks and spurwing). On a recent blue duiker hunt I switched chokes to IC/M (invector plus chokes) and the shot pattern was still relatively tight. The choke and shot combination should be considered in light of the anticipated shot distance.
In terms of stock shape, I find the straight stock and round action carries much easier than my Browning O/U. However, as mentioned, stock fit is the most important factor. Prins of Wales is the best of both worlds.