Let's not overlook possible reduced mag capacity when using the longer shells, it's a factor to consider. It's just one reason most folks stick with 2 3/4-inch shells.
Define suitable for self defense load. Is your neighborhood plagued with 350 pound heavily armored meth head axe killers? Just curious because if you are could I suggest an 8 gauge.Any factory produce 3½ inch 12 gauge loads with 00, 000, or even 0000 buckshot suitable for self-defense loads ?
Hearing about some of the violent home invasions and the types of folks doing it, not sure anything is too powerful.