I was thinking about using that same exact one Dr. but i figured for my situation i am going to need a 6" because the carbon scrubber is going to reduce my cfms and if im only working with 80 to start with i figure there wont be much left after filtering. The 6" i believe moves about 180 cfm anf the 8" about 250 cfm if i am correct. I would however use the 4" for my intake. I would go with the bigger one for exhaust, if it gets to the point where it over cools for you, you can always put a rheostat inline and control your fan speed with it. Hope this helps.

Blaze is the howl coming from the motor or the fan blades,can you tell?