Im going through the same thing with a similiar room.but it matters how u have your air intake and exhuast set up?air cooled hood or not?u should be venting the scrubbed air out and away from the room your set up is in ie. window,dryer vent,chimmny ect...And from what i was told bigger is better with a speed controller.remember and a carbon filter,bends in the venting and long vent runs are gonna reduce the effectivness of your fan....so a 6" 400cfm is gonna be less then advertised.sorry for the long winded answer,hope this helps