I shoot both ITX (Roll my own) and Hevi-Shot for years. I shoot Hevi-Shot for waterfowl and turkeys. I shoot Hevi-Shot 6's for ducks and 4's and 2's for geese in a 12 and 20ga. Both are shot with a Briley Ext. Ported Imp. Mod. DEADLY!!!!! It will pattern like a lead Full plus. Ducks and geese just flip. Almost too tight for most to shoot. I have patterned it extensively and really like it for what I do.
I shoot the same choke for turkeys and go to 3"-6's and 3-1/2"-4's for back up. Smashing out to 40+yds.
I have shot ITX for my waterfowl for 2 yrs now in my 20ga O/U with great success!!! I roll my own 2-3/4" with 7/8ths oz of 4's for 1st shot and then a 3" in the other pipe of 2's. First shot is in Mod. tube and the other is Imp. Mod. Both Briley ported. I shot 17 Canada Geese last year in Alberta for 20 shots in a 20ga with ITX!! Closest was 7yds and the longest was just a tad over 50. Witnessed by 2 other guys with me. And the long shot was after a guy missed with 2 loads of Steel 1's and BB's.