I love you; Is there a way to give you reputation on this board?
You can select something someone says as the "best answer" which gives them points on the board, sort of like reputation.
I think the RC-690 has pretty awesome airflow to begin with, it can utilize 7 fans all-together, so you could maybe add a fourth to the side if you want. Ideally you want negative pressure in the case, meaning the airflow out is higher than the airflow in. You can just add the cfms of the respective fans to figure it out. Negative pressure causes cool air from the room to be drawn in through vents, and helps the circulation process.