Steel is steel no matter what load you use. Unfortunately, those expensive no-tox loads do work much better than steel. Regarding Hevi-Metal, don't bother. Myself and two friends tested some Hevi-Metal high-velocity 12 GA #5's in a GPA (public) unit last November on pheasants, and they did a very poor job killing birds, even as close as 30 yards. We later switched to some Kent steel 5's and even they worked better.
My favorite no-tox shells are the Hevi-Shot 1 1/4 oz #6 loads made by Remington a few years ago. I only have a few boxes left, but these kill birds like plated lead shot. However, HS must have a different formula now than what those Remmy loads used, as the new HS loads are reported to not work as well as the original........