it doesn't really matter if you intend to overclock or not- it is always good practice to have optimum airflow in your case as every *C less will prolong the life of your components.
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could I have all 6 fans set up as intake or exhaust, as in 6 intake OR 6 exhaust?
That would just trap and circulate hot air within your case. best setup would be 3 exhaust rear and top and 3 intake front.
I'm curious about a 6 exhaust setup though as i have never personally tried such an exhaust only setup except on old pc's that only had space for 1 rear fan at the back..