Well, there is always debate over which is better, 3 or 3 1/2". So, I went to Federal's website and checked out some numbers. I looked at the Federal Premium High-Shock Lead High Velocity. Sounds like a good turkey load to me. This is interesting.

3"--- The muzzle velocity is 1300 fps. Dram equivelancy is 4.19 dr. and the shot charge is 1 3/4 oz.

3 1/2"-- Muzzle velocity is 1300 fps, Dram equivelancy is 4.57 dr. and the shot charge is 2 oz.

As you can see....you gain absolutely no power at all. Speeds are the same, energy the same, everything. The only difference is the amount of shot which needs more powder to push. This equates into you getting knocked over and a turkey that is just as dead as it was with a 3" shell.