WTF are you building??!! An airplane?! You should look into something called "liquid." haha. That sounds sick though. If you had a bad *** looking case and all with four of those mega fans inside.
And dont be fooled...2 65dB fans does NOT = 130dB so dont worry. In order for something to so "sound" twice as loud, its source needs to be multiplied by a factor of 10, not 2. I'm in AP Physics, 4 fans @ 65 dB would only be about...80db
65 dB would only be as loud as a piano or people talking...not a vacum cleaner. but seriously thats still insane.