It depends on what you are using your computer for. Clock for clock even if a Q6600 is run at the same speed as a E8400 the E8400 will still be faster in single threaded programs that dont take advantage of multiple cores becuase it has more cache 1 mb more per core.
If you plan on gaming, the E8400 will be a much better choice since it runs 3ghz stock and it uses 45nm which make the E8400 generate less heat, If you plan on doing photoshop and encoding then the q6600 will be better
i would go quad because more and more games r taking advantage of more cores. so u would be future proof thats y i picked up the q6600. i have mine oc 3.0ghz at only 34c idle 45c load stays cool. even tho ur not oc i would still recommend the quad. when 4 cores r being utilized i dont care how much the 8400 is oc it cant take down the quad.
on the other hand,and just to muddy the waters a bit,more and more proggies,including games will/are going to take advantage of multi cores,like alan wake,for instance,probably by early next year we will see more of this trend,,kinda hard not to overclock when one has a cpu that can take it,,eh what??:>)
stock fan is fine if you do not overclock. You can even do limited overlocks with a stock fan, aftermarket fans are good and are great/basically required for series OC but if you are only runnin stock they are all overkill.
Aslong as you correctly install the push pins by checking the backside of the motherboard that the pins went all the way through and are locked stock fans do there job.
+1 for E8400. Its cooler, higher FSB, does better in every current game including the Unreal 3 engine and a lot of games in the near future will use it. It also has SSE4 insrtuctions which future games will use and will bring another nice performance boost.
Stock fan is fine even if you mildly overclock. Theres no reason not to mildly overclock, most boards ave a oc profile built in to the bios or come with software to overclock. As long as you dont go over 3.2 on either one you'll be fine.
if this is only a 3 year build go for the dual core. if you want it to be viable in 5 years get the quad.
5 year plan would be to use the stock fan for the first 3 years, then replace with decent cooling fan and lots o ram so you can overclock it then. you may not want to OC now, but in 3 years when you can jump from 2.4-3.6Ghz for the cost of a cooler you'll want to.