Well, a little math here... for a target crossing at 90% traveling 60fps (about 40mph) 40 yards away, a pattern travelling an average speed of 1500fps = 4.8' of required lead. The same target shot with pellets averaging 900 fps = 8'.
Now, for the same taret at 16 yards, 1500 fps = 1.9' vs 3.2' for 900 fps. So, for skeet ranges, it matters a foot or so (or 50% of your lead).
What really matters for ducks and flying critters is air speed + wind speed. A bird flying slow with a 30 mph tail wind can be tricky to hit.