Sporting Clays is my weak link as an all-around shooter, but I have used a good bit of spreaders in 3Gun, and patterned them. For Mod and IM chokes, they have given me about a 25% larger pattern at 18 yards, for full, about 30% larger. Past about 25 yards, too many holes IMHO for sporting clays. I typically use them in 3Gun when there are close open static clays (5-15 yards) and some longer shots where I want a Mod or IM choke.
I am resisting changing chokes and only use Light Target loads for Sporting Clays. I want to get as good as I can without fiddling with loads and chokes, even though I understand how they can benefit. I heard two quotes from accomplished SC shooters this past week...
"If you can't hit everything with a skeet choke, you are doing it wrong." and "If you need anything besides Mod, your leads are wrong." Both make sense.