I plan to install a second 140mm on the top blowing out and two 120mm's on the bottom blowing in.
Would this provide good circulation for a cooler system and should i install a side fan or a better heatsink such as a Zalman 9900?
My setup is- -Intel i7-920 (May be overclocked slightly once i am sure i want to and know how to) -ATI Radeon HD 5850 (May Crossfire in the future) -Asus P6T Motherboard -OCZ 3 x 2gb 1600 DDR3 -Corsair TX750??
Are these enough fans to cool my system and does my setup provide good circulation? and also is the 750w a good choice since i may want to crossfire in the future?
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Honestly adding the extra fans WILL help with airflow, but im not sure how much of an increase in cooling you will actually see. Probably less then 5C in all likelihood.
Your best bet is to get a better CPU Cooler, like the megahalems or NH-D14. The Zalman is OK.
The optimal position for fans is Front IN, back OUT. Top fans usually blow up (no pun intended) to exhaust heat as well.