There were pictures posted on another frequent "whats the best gun" thread that showed various calibers punching through simulated intereior walls. 00 buck went through 4 sheets of drywall, and the resepctive 10 feet of space between them, with ease.
I recommend #4. It will kill and not easily pas through interiors.
And you get 27 - 0.24" dia. #4 buckshot instead of 8 - 0.36" dia. shot in a 2 3/4" shell. Dixie that is #4 buckshot, not #4 shot for waterfowl.