A "sporting" gun should work well in the field since the whole idea of sporting clays was to mimic actual field shots.
2 3/4" is about all most of the people I know use for hunting upland birds (pheasant, quail, grouse, prairie chicken, partridge, etc.) Most do however step up to 3" for waterfowl, really made almost necessary by steel shot, but with the newer "heavy" nontoxic shot 2 3/4" will work fine unless you are trying to do some "skybustin" on high flying Candas. If you do use the new nontoxics be sure to test pattern them with all of your tubes, due to their density and hardness they respond "differently". This is necessary, but not cheap to do, they run about 3 to 5 times the cost of a box of AA trap loads for a box of 10 shells. If you want to hunt turkeys, again 2 3/4" heavy load of 4, 5 or 6 shot out of a full or x full tube will do a number on them. The new 3" or 3 1/2" turkey" loads are not necessary (and not much fun to shoot when you are sitting against a tree.)
For about 25 years I used one shotgun, a 2 3/4" chambered modified choke pump gun for hunting all of the above, and goose hunting was the only time I could have needed more.
bergie