the only way to see what works is to put alot of time in at the range. I went probably 10 times the month before spring turkey season trying all different combinations of chokes and ammo.
on my Remington 870 20 gauge I stuck w/ a Primo's Jellyhead choke and 3'' Winchester double X turkey loads. I also like Hevi-Shot Magnum shells. They both shoot really tight patterns out to about 40-43 yards; which is way beyond what I even feel comfortably taking a bird.