Hi,

about your concern, it happen to me recently too. Leaving me wondering whether to buy Quad or Duo. At the same time, price of the processor also is taken into consideration making it more and more difficult to choose a product. I went to tomshardware.com to search for answer as there are many articles on it. Let me summarise what i had read.

When using processor, the below things is taken into consideration.
a) Application that can run multiple core or single core.
b) price of the processor
c) future consideration
d) overclockking

a) multiple core application
===================
This is very important as it will determine the effectiveness of your processor usage. If you application is only design to run single core and not multiple core, then quo core is not better than duo core with the same clock frequency. Meaning if you have quad core 2.6Ghz and a duo core 2.6Ghz running a non-multiple thread application, there is no different at all. But if you put a multi-thread application into runs, then there will be significant increase of performance at least 15% and above over duo core processor.

Even a E2160 over clock to 3.2 can have the same performance as a quad core 3.2ghz processor if the application doesn't support multi-thread. Believe it or not, but reality is so.

b) Price
=====
a Quad core on lower speed is definately expensive than a duo core with high speed. This is because quad core include more transistors in it. So the main concern in purchase processor is whether u willing to put more money on lower speed quad core processor and not be able to fully maximize the usage of the processor OR you willing to give up the technology of quad core and go for more practically processor (duo core) which every application can benefit from it 100%. if you check the price, Q6600(2.4) is RM680 but E8400 (3.0) is RM590 at the moment. So you need to be wise on using your money. Until now looks like you are influenced and have more attempt toward duo core....which is cheaper yet can fully utilise and faster too. But wait till you read the next paragraph.

c) Future Consideration
===============
Even though duo core is faster in many application compare quad core on the same PRICE Product, meaning Q6600 VS E8400, Q6850 VS E8600 (similar price product) BUT this might not be through in the future as more and more application is been written in supporting multi-threading. Don't every compare Quad with duo core for the same clock frequency as quad will always win. What i am taking is similar price product. Okay...going back to future consideration, games, 3D application is starting to using multi-thread technology and begin to utilise the quad core processor. For those application like office and DVD burning that dont use multi-thread , ...by the way we dont care so much....because we dont need such a fast processing for those appplication as it already can run very fast with low end processor such as E2180. So at this point is better to have quad core over duo core now to be ready for next generation application. Believe me with an application supporting multi-thread , Q6600 (2.4) can be faster thab duo core (3.0) with at least 10% different. That is where allyour money pay off.

d) Overclocking
===========
This is the main part and must not forget topic to be discussed. Quad core has more overlocking power compare to duo core. Why ? at duo core you only have two core to do uppgrade, whereas in quad core you have 4 core to upgrade. You heard "sikit sikit lama lama jadi bukit" theory" This is what happen to 4 core processor. And also if you think current application doesnt support 4 core, but require more clock frequency, then just overclock your quad core processor comparable to duo core processor that your intend to buy. But the risk is you going to void your warranty if any things happen. but no worries, many ppl over clock the processor easily and still not damage the processor. JUst remember ...DON OVER CLOCK it....


Conclusion
========
okay dude, i have been talking to long....hope this summary can help others saving hours and hours of time searching for answer.
Thanks.