The goal is to exhaust slightly more air than you bring in. Since hot air naturally rises, a top fan is a good thing as long as you have some top clearance. Bottom fans bringing air in are also good except if you are like me and have the case on carpet or have pets (6 cats in my case). Bottom fans will suck dirt from the floor and filters do not off set the issue. So in your case (got to love the pun) I would add one intake to the side and another in the rear (exhaust) if I had the room. I have a 1200 with the 3 in the front (in); 2 in the back (exhaust) running at their lowest speed. The top fan runs at it's mid speed. My side vent ins passive as my cpu cooler will not allow a fan. It shows dust on the outside of the filter indicating I am exhausting more than I am bringing in.