From my experience, apartment walls are usually thinner than home walls, so you'll want a lighter load than what you'd use in a house. The good thing is, a confrontation will usually be a lot closer in an apartment than a home. So the shorter distances should be able to make up for the decreased "stopping power". I would get some #4 heavy game loads and do some of YOUR OWN pattern and penetration tests. After you've viewed the results and have come to your own conclusion, stick with that load, or move up or down shot sizes accordingly.
"Those that would trade essential liberty for temporary security deserve neither liberty nor security."-Ben Franklin
Woe to those who make unjust laws and to those who issue oppressive decrees. -Isaiah 10:1
Blaming guns for death is like blaming forks for obesity