2 3/4” 7/8oz 71/2 lead for partridge and quail, or even pen raised pheasants. Anything more is a waste, they are easy to kill.
Bigger grouse, chukar, pheasants, etc 2 3/4” 1oz lead 6’s is plenty out to 38-40 yards, which is a poke with a shotgun. 99% of the people I see shooting past that distance are wounding and not recovering half the birds they hit at that range anyway, even if they are gunned for it. Dont be that guy.
3” 1 1/4oz lead 20 ga generally pattern like dog doo for wingshooting, you gain nothing over a 1oz 2 3/4” load except recoil and cost—they dont pattern or kill one iota better ime. Save those for turkeys where the denser core of the pattern will actually be helpful. If you are handloading I have spoken with a very few people who would know better who say they’ve had ok luck with a 3” 1 1/8oz load of lead shot. But in general the very long shot column of a heavy 20ga creates a ton of flyers so the fringe of the pattern falls apart pretty quickly, they just havent been helpful for me.
If shooting steel the standard rule of thumb is to go up 2 sizes from lead. Steel is the only application where Id even consider a 3” shell, as the harder shot doesnt deform so there are far fewer flyers.