It's one of those things that without some pretty impressive camera equipment, we'll never know the answer to.
I have pattern tested a few steel game cartridges in the past through 1/4 choke and I was quite disappointed in just how big the gaps in the pattern were for a 32g steel 4 compared to a 30g lead 6, easily enough for a smaller game bird to be missed when the ranges were out past 40 yards. I would imagine that a lead 7.5 or 8 would present a pattern that is a lot more populated for a lot longer.
Given that both the shot and target are continuously moving relevant to each other, I'm not sure how effective pattern testing really is.