Oh boy.
This is a much discussed topic.
I considered this long ago.
I'm using an 870, full choke, 1 in the chamber and 6 in the tube. And an 18.5 inch barrel.
The max straight line distance in my house is about 65 feet. Worst case scenario. If I was to use 00 buck at 65 feet, there's not a lot of room for aim error. A few inches off target and I would miss. Complicate that with a darkened room and adrenaline pumping. This is why I choose to use 0000 buck in a 3 inch load. Max capacity and denser pattern. I tried both on a pattern board and made this decision based on what I could expect from my gun and ammo. And we humans are rather thin skinned. It only takes 1 or 2 pellets to make an impression. Even with thick clothing and a jacket.
Your milage may vary.
EDIT:
Ok. Not 0000 buck. Should be #4 buck. You caught me.