You also have to realize there are different fan sizes. I highly doubt your friend had 120mm fans in his case, they all sound like 80mm ones. 120mm move a lot more air a lot more effectively than 80mm fans, plus they are quieter.
You also want more fans exhausting than intaking to prevent air pressure build up.
In my opinion, all you'd need is one 120mm front intake fan, one 120mm rear exhaust fan, and maybe a top exhaust fan. If you're really looking at nine possible system fans you may as well consider water cooling. :P
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