1 & 2 shot for the longer shots
Also pattern your gun/ chokes and shells
My guess your mod or Full will be better for longer range

But here is my $.02 for what is worth

You are going at it all wrong IMO

If you have to take longer shots
Your 2 3/4" loads will scare and cripple more birds than you will reduce to bag
Making it harder to get birds even that close next time and for others

Also other hunters will resent your sky busting , for scaring the birds and not hitting anything

It is cheaper in the long run to shoot a proper load
A 3" 1 1/8 oz of #1, #2 in a pinch at 1500 fps or faster will result in more DEAD ducks per box
If you can shoot that far repeatable

I have found it is much better for all to find a place that takes more work to get to
So the birds will decoy into reasonable range

Also You might end up with more birds with less shots
Even if you only get 2 or 3 birds to decoy

Because I have seen sky busters shoot 2 boxs in a day for 2 birds
While I take 3 shots for the 3 birds that I got to decoy , with 3 birds to show for my mile+ walk

John