What Oldtimr said, or borrow a few different brands, loads and pattern them. Even try changing chokes (full, x-full or even modified) and see what combo patterns best in your shotgun. And ALSO HITS WHERE YOU'RE AIMING.
Once you find what combo your shotgun likes the next step is to determine how far that load will pattern for an ethical kill on a mature tom.
I have a little Rem 870 youth model 20 gauge that will, with 3" Winchester Supreme #5 shot, roll a turkey flat at 40 yards. But I like to get them much closer and sometimes I've let them get too close.