I've used a 20ga 870 Remington for ducks for at least 22 years. I hunt both timber and fields, probably 45 days per year. My favorite load is #2 shot in the black cloud 3" load. IC choke for timber usually, but sometimes I use MOD. In fields i always use MOD. 20 will kill just as well as a 12 imo. I bought a new benelli m2 camo for ducks last year but i don't particularly like it so gave it to my son and back to the 870. If you can keep your shots inside 40 yards you'll be fine. Sky-busting with a 20 is just a waste of good ammo. As always, ymmv.
