The state regulations here allow #4 shot as the largest size for turkey, they have no minimum size.
I've used 4,5, or 6 shot depending on the conditions. This year I will likely be using #6 as it was an early spring and the woods should be leafed out pretty well. They will fill out a more open choke which I use after the woods leaf out. If it were a more normal spring the visibility would be much greater and I would most likely load up with 4s and a more typical choke.
