Don't you need to get air out of the case as well? I would think that would be even more of an issue than getting air in.

Agreed, and I am trying to plan for a proper airflow scheme that combines pushing and pulling to get the best available cooling while still remaining as quiet as possible. Taking into account all the factors, of course, such as which things generate heat, trying to make sure not to pull hot air over something that's already hot, etc.