I have several turkey guns in my arsenal that I have collected over the last few years. 3 are Remington 12ga's they all have 23" barrels, 1 is a Browning BPS 10ga w/ 24" barrel, and last is a Browning Gold Auto w/ a 26. All are 3.5 inch shooters and all pattern about the same. It is just my preference, but I wouldn't go any longer than 26" barrel. With todays chokes and loads you can get a really sweet pattern out of a short barreled gun and they are so much more handy in the field. That is just my .02!

Shoot what you like and shoot it well and you will be knocking birds down without any trouble.