4" fan for cooling multiple hoods

I'm looking at this light for my 600w HPS lights:

http://aeroponicsnmore.com/lighting-equipment-reflectors-hoods-c-1_9/supernova-aluminum-hps-or-mh-reflector-p-90

Everything looks great except the flange size: 4". Is a 4" fan enough to cool a daisy chain of lights adequately? I'm not sure how big my setup will be yet but I'll probably have 4 minimum, 8 max.

I would go with a good 8" fan, it is better to have to much air flow than not enough.

4" fans are antiques. minimum now is 6".

I use a 4 in it works perfect for my attic setup.

can a 6-8" fan even be used here though?