I tried two in there clone, if anything they interfered with front air intake. My current setup is.
x2 sp 120's front intake
x2 sp 120's on hdd cages
x2 sp 120's top exhaust
x1 af 140, rear exhaust
x1 alpenfohn red clover at bottom exhaust.
x2 2350 rpm PWM sp's on the cpu cooler.
I only stuck the alpenfohn in as it matches the build theme. Very slow fan that doesnt shift much air.