Most kills will be in the 20 yard range anyway, which shouldn't be a problem with standard loads. Just make sure you shoot paper a few times and know where your POI is, and how far you can shoot without the pattern breaking up too much.
Saying most kills @ 20 is a giving a false sense of hope while playing the game.... Yes a person can get lucky and have one walk in that close... Out of the dozen+ I have killed only 1 was 20 yards or less (16 paces to be exact).... They don't always get that close for whatever reason.
Alot has to do with the area your hunting.... thick woods, open hardwoods, or fields/pastures.
As was said, shoot the gun, check the POA/POI, and determine the effective range for your barrel length/shell/choke combo.... then hunt and try to get your birds within that effective range... If you try long enough and are not satisfied with the results.... you can always buy another gun with a larger chamber.
I would rather have a gun set up for distance and not need it, than to need it and not have it.... Turkeys have their own schedule and you can't make them do something they don't want to....
I have limited time to hunt, spent hours at the target range testing, spend money on shells, license, gas, equipment, and calls..... I won't be going home empty handed unless all other options have been exhausted.