If lead is not legal were you hunt then then I would go with some other non-toxic shot for turkey, like tungsten. Sure it’s expensive, but your don’t need a lot of rounds to bring down a turkey and you can only shoot a handful of them each year.
I can’t remember for sure but I think my full turkey choke on my 870 says it can take steel shot, but I’ve never tried it. If you find a turkey choke that can handle steel I would definitely pattern it. Seems like that combo would have some blown out patterns.
Steel works just fine for turkeys. I‘ve used #3’s to kill a couple Turks in the wildlife area. Yeah, other non-toxic would be most bestest, but it’s what I had on me when opportunity came knocking. Know the limitations and work within them.