Ok, a couple of tips...(some might be in the FAQ...I didn't read it
1. Get it out of the cubby hole. When a rig is put into the "nice, convenient" cubbies that desk manufacturers make, it will usually hurt the cooling. This is because the warm exhaust air has little or nowhere to go and simply pools around the case only to be sucked back in.
2. I am not sure why the top/bottom + front/back would be seen as self cancelling. Yes, you will have a kind of intersection in the middle of the case where the incoming flows will collide, but this will only cause turbulence (a good thing). The exhaust fans will draw whatever air is available and will not cause compartmental flow conditions, if that is in fact what people are concerned about.
3. Have more intake than exhaust. The PSU needs air as well, you don't want anything "fighting" for air. This will also help reduce compartmental cooling as higher pressure helps promote turbulence which in turn reduces streams (paths of dierected/organized flow).