finally a casefan that is sufficent
 

surprisingly such a fan disrupts airflow completely, making it far from ideal for optimal airflow; older review with similar large side panel fan: http://www.madshrimps.be/?action=get...&articID=4 22

or more recent one with 4x120mm in side panel:



http://www.madshrimps.be/?action=get...&articID=5 26

This is really the biggest side fan I've ever seen. But like jmke already said: an airflow from front to back results in better temperatures, espacially while using a tower cooling unit for the CPU :)

not only the CPU matters for cooling but how would it help the temperature of all the components on the motherboard or the PCB of the GPU

Well I think the mainboard components would stay abit cooler, but on the other hand there will be big problems with airwhirls while using front fans next to that 400mm one; and without those the harddisks will get hotter on the other hand :)
For the gfx card a smaller 120mm fan in height of the PCI-E slot should be enough.