For many years I hunted turkey with an old Double Barrel Stevens loaded with #5 Remington 3" Nitro Express. I always limited my shots to 35 yards and never had a problem knocking one over.
Now I hunt them with a black powder shotgun and limit my shots to 25 yards because it is a 20 gauge (.62 caliber smoothbore).
All this is going to change though. I just ordered a 12 gauge extra full choke barrel for my Thompson Center New Englander. They claim this is an easy 40 yard gun. Time will tell.
With what you're shooting I would think a 35-40 yard shot would not be impossible. Best thing to do is set some card board boxes up and check your pattern at different distances. Also hang a tin can inside the box, like what you get vegetable in. If the shot penetrates that can, it will kill a turkey, or at least penetrate him. You have to place the shot.