FYI...the idea that longer barrels equates more range/speed/power comes from the days when it really did make a difference. The powder used today is different from the powder your grandfather shot. Back then the powder didn' t burn as fast as it does today, so they needed the longer barrels to contain the explosion for a longer period of time. It was especially important to the waterfowlers back then.
Like Strut & Turk-man said not much. The biggest effect barrel length will have on your gun its balance & handling. Maybe something to consider if you plan on using the gun for wingshooting in addition to turkeys. Then there' s the weight issue. If you don' t need the extra weight, don' t get it. Bottomline...26" will do fine.