I have been turkey hunting a 12ga since i was probebly 10 years old.I started out shooting the 2 3/4 in. mags in a semi auto,then when i was 11 i steped up to 3 in. mags in a 870 and now i shoot 3.5 in. mags out of a 870.I would go with what ever was most comfortable for you,whaen that turkey is standing up there you wont even know that you shot.

Hope this helps and good luck this spring.