I would also be concerned with an AMD FX octo setup blowing warm air across the VRMs...
GTX - it creates FLOW. While there is some 'fighting' for air, it still creates an optimum airFLOW through the case In that air goes out the top and rear while fresh comes in the front/bottom/sides. If you are concerned about dust, than having an unfiltered intake located anywhere totally defeats the point of filtered intakes, I agree. I should show you the cracks of my case, there isn't anymore dust there than when I ran it with more intake than exhaust. Perhaps it was just my case (or two) and how it was setup, but those were my experiences. My biggest hangup with more intake than exhaust are the hotspots it can create because it isn't taking out the warm air fast enough. In an old case I had sensors everywhere testing things out. It wasn't until I went more exhaust that I saw the best results... this was with 5-6 sensors around the case (intake air, exhaust air, intake rad spot 1, exhaust rad spot 1, intake rad spot 2, exhaust rad spot 2).
Well, it is a case by case basis I suppose. In all my years on forums, in all of my experiences, I will still stick with more exhaust than intake for best overall results (includes case temps).