Which refelctor is better?

[Killertea08]

What reflector would be better guys? Im growing in a 4x4x4 box that would be 16 sq/ft and using an air cooled 600w HPS lamp so that would give me close to 40watts per sq/ft. The question I have is really about heat. I can either get a reflector with a 6" flange or an 8" flange. I understand why I would get the 8" flange to obviously pull more cool air through but would it really matter that much? Im worried about heat build up.
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[The Hemp Goddess]

I really think that you should be able to control the heat with the 6" flange. A big part of the equation is the fan you use to cool the hood. When you double the diameter of a circle, you 4x the area--so a 6" is approx twice as many sq in as a 4" and the 8" is double the sq in of the 6".