Cabinet grow, too much air flow? carbon filter

Scaling down to a custom cabinet is proving more difficult than a full grow room for me anyway. I have a box that is roughly 7 cubic feet. So if my math is correct I need at least a 35CFM exhaust fan to clear it properly. I will have passive light trapped intakes down below. The box is quite sealed as well. So.. here's my issue... I have a 35cfm fan and an 85cfm fan in my hand. Both are 4" Dayton brushless axial fans. Basically large computer style fans. They are rather quiet. I plan on putting a carbon filter on the box if possible. What fan should I go with for exhaust with a small scrubber? Will the 35cfm fan be good enough or should I go with the 85cfm fan to be safe? Is it overkill?? And does anyone know what the best filter is for a square 4" Dayton fan is?
 
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