None of those options, you have to control airflow to push fresh air into places that need cooling, or to suck out the exhaust of heat producing devices.
Case manufactures can only go so far because of the need to remain compliant with a broad assortment of hardware, so they mainly go after the wind tunnel effect(creating an airflow front/low to back/high) with little regard for noise control. As far as whats better for this wind tunnel effect, neither just CFM.
BTW if your temps drops when opening the side panel then you need to rethink your design.