And as per a Matty special request, i have arrived..
For you with the Antec 900 you won't notice much difference by using 2 fans as opposed to one, as there is plenty of room for the air to be dispersed.
Now in my case (no pun intended
), my lil' Lian Li A05 has,
TBH, quite limited airflow, even with the blowhole mod, so anything that can help the airflow to be laminar through the cooler and spend as little time inside the case is a big bonus.
Also, the 2 fans help to disperse more air from the PWM and MOSFET coolers, as there is essentially, more active airflow going over them as they are on both sides of the cooler.
Basically, using 2 fans doesn't put much more air through... it just means that the air is kept laminar and therefore the heat spends less time in contact with components before it is exhausted.
So in essence, what i am saying is, if you have decent room in your case, then there is no requirement for dual fans in push-pull.
For cases with more impeded airflow, it can help to keep things running smoothly.
One thing you shouldn't do is put 2 different fans on it... Otherwise the fans will end up battling against each other and cause more heat, i run both of my fans off a fan splitter cable, and use high quality fans, so that:
A: both fans spin at the same speed
B: it is nice and quiet
C: see B
So unless your going for the top O/C then 1 fan is fine, and cheaper