I shoot sxs's in the uplands. In the early season when there's more cover and the birds sit harder, I tend to select IC/M. Later in the season when the birds are coming up further away, I switch to M/F.
Shot size is also part of my calculus. For tough species like Sharptail and Pheasant, I use #5 shot in the more open choked barrel, and #4 in the tighter choked barrel. This works well for me because the birds get just as dead, but are hit harder by far fewer pellets. Hence less damage to the meat.
For more delicate species like Ruffed Grouse or Gray's Partridge (commonly known as Hungarian Partridge or simply Huns), I use #7.5 shot in the open choke and #6 in the tighter choked barrel.
This strategy works so well for me that I have no reason to experiment further.