Don't worry about the chest thumpers who are afraid that anything less than a 3" 12 gauge slug will only irritate a bad guy poking around in your jewelry box or unhooking your flat screen TV. Nobody wants to get shot and at in house distance even if you do not kill them you will make them try to find another address besides yours to lick their wounds in. The dead ones you will find in your yard the live ones the police will pick up at the local Emergency Room begging for drugs while the staff ever so gently plucks little round balls of lead from their hide.
I use #4 shot myself because I do not want to penetrate the walls of my house with slugs since I have family on the other side of the walls. I use slugs in my 20 gauge for deer hunting but I am talking about 60 to 100 yard deer not boogerman at 20' or less. I have slugs of various and sundry types and brands, 00, 000, #3, #4 shot, #6 shot, 7 1/2 shot and #9 shot for my 20 gauge but I use #6 or #4 for turkey and home defense. It is what I am comfortable with and if #6 is all you have you are not unarmed.