It's really trial and error. Shoot a bunch of paper targets with different loads and chokes if you can. If not use a standard full choke and know the limitations of your gun. If it only patterns good at 30yds don't shoot anything farther than that. The guys here seem to want to find a load/choke combination that will reach out and touch a turkey as far out as possible,but many birds have been killed at 20yds. For this you don't need anything special. Remember that with a x-full choke that patterns really well at 40+yds your pattern at 15yds may be slightly larger than a slug. You could very well miss your target. So the question is ... How close will you be to that bird when you shoot it?