I know you said steel shot, but I bought a bunch of 12 ga. magnum 1 1/4 oz Bismuth shells to shoot ducks with my old Lefever double gun. The magnum Bismuth ended up being too hot for my Lefever so I used it up shooting ducks with my Ruger Red Label.
I'll tell you what, even though they cost 2-3 times as much as steel shot, I felt it was a break even proposition because they were much more deadly than steel shot for me. No more sluicing a bird two or three times, ducks folding up and falling dead in the water like the old lead shot days. You have to adjust your lead because the Bismuth is slower than steel, but for me, that means I'm shooting the same speed shot all season, ducks, pheasants and other upland game, so no more relearning my lead when I switch from waterfowl to upland and back again.
I'm not sure I would buy the more expensive Bismuth for my modern guns, but if it went on any kind of off season sale, I would think about it. I will be buying a lot of 1 1/8 oz Bismuth for my Lefever though.