I haven't shot a lot of ducks with TSS, but I have killed a few and other hunters in my group have killed more. We used #8, and I can't see any reason to go any larger. Stan, shot in the breast was not an issue; got complete penetration on all hits.
The biggest problem I saw with it was that patterns were just too tight. Even with a cylinder choke, I got 87% inside a 30" circle at 40 yards. I had to put steel in one barrel for closer shots and use the tungsten loads only for longer shots.
There are some recipes for duplexing tss with steel that I would try if I were ever in a position to do a lot of duck hunting. I'm not sure that tss alone is a very practical duck load.
