Sorry..............,
I disagree with many of you where ducks alone are concerned. We have been using Kent Steel for a number of years.
23/4" 12Ga.-1 1/16 Oz of #2 or #3 shot. Also,
3" 12Ga. 1 1/8 Oz of #1 shot.

The 3" #1 shells are death on late season mallards out to 40-45 yards.
The 2 3/4 #2 shells are fine for 30-35 yard shots
The 2 3/4 #3 shells are fine for over decoy shots out to 30 yards.
There is no doubt that the Kent loads have the juice and power for deep penetration on late season mallards out to 45 yards.( November/December in Canada)
Out to 20 yards we often have total penetration and exit with the #1 shot in the 3inch loads on late season mallards.
With good hits out to 40-45 yards, we get as high percentage instant kills as we did with lead.

All distances I talk about were verified with Laser range finders, on flying birds with the continuous read out mode. One spotter and one shooter. The moment of the shot signalled the final reading.

I like steel on ducks because it has been proven to us that it has the required energy out to 45 yards,and because of the affordability.
I am not disputing that tungsten/polymer, heavy shot and bismuth are much much better at longer range.
At what price? and.........................how many of your ducks do you shoot regularly and with consistency in centre hits over 40 yards??? Its like asking how many % of your deer do you shoot over 400 yards?

My observation is that many handicap themselves by shooting way too tight chokes with steel. Its that old inbred thing that we gotta use tight chokes for ducks. Steel changes that equation.
In the lead days there was a lot of sky busting going on, with the odd one flooking out. Steel indeed looses its velocity and power a lot faster then lead as we all know. If you try the old sky busting routine with steel you be subsidizing the ammo dealers.
However most ducks in my life have been shot well within 30-35 yards. I regard 45 yards as max. for my ability to consistently produce good centre hits.
Modified(21-25/1000) is plenty for my gun/choke combo 35-45 yards.
Skeet(4/1000) is great over decoys with #3 out to 25 yards ,and IC(12/1000) does fabulous with steel out to 30 yards . Numers are in my gun and choke combos alone, not necessary in yours.
Trying to hit 10-20 yard ducks with a modified chokes and steel loads is very difficult and unforgiving, due to the tiny pattern.
Check some patterns in your gun and open up on those chokes!!!. You may be surprised.

I have not hunted many geese with steel. For the big Canadas we use "something different" out here.