I handload a 1oz load of Hevishot #6 for my 20's for ducks. Works great.
If geese are in the picture, I use #4 Hevishot.
Hevishot is the reason I do not own anything but 20ga guns at the moment.
I typically use IC in both barrels, though I will also use CYL in the right and IC in the left on occasion.
Yes, it is not cheap, but how many shots are you going to take in a day?