First, I could not ask this on most hardware forums, because they are mostly populated by gamers. Additionally, it is difficult to get an opinion from sysadmins, because they have a fairly different perspective as well.
So perhaps, amongst developers, I might be able to deduce a realistic trend.
What I want to know is, if I regularly fire up netbeans/eclipse, mysql workbench, 3 to 5 browsers with multi-tabs, along with apache-php / mysql running in the background, perhaps gimp/adobe photoshop from time to time, does the quad core perform considerably faster than a dual core? provided the assumption is that the quad has a slower i.e. clockspeed ~2.8 vs a 3.2 dual-core ?
My only relevant experience is with the old core 2 duo 2.8 Ghz running on 4 Gig ram performed considerably slower than my new Core i5 quad core on 2.8 Ghz (desktops). It is only one sample data, so I can't see if it hold true for everyone.
The end purpose of all this is to help me decide on buying a new laptop ( 4 cores vs 2 cores have quite a difference, currently ).
http://www.intel.com/content/www/us/en/processor-comparison/comparison-chart.html
I did a comparison for you as a fact. Here Quad core is 2.20 GHz where dual core is 2.3 GHz. Now check out this comparison and see the "Max Turbo Frequency". You will notice that even though quad core has less GHz but when it hit turbo it passes the dual core.
Second thing to consider is Cache size. Which does make a huge difference. Quad core will always have more Cache. In this example it has 6MB but some has up to 8MB.
Third is, Max memory bandwidth, Quad core has 25.6 vs dual core 21.3 means more faster speed in quad core.
Fourth important factor is graphics. Graphics Base Frequency is 650MHz in quad and 500MHz in dual.
Fifth, Graphics Max Dynamic Frequency is 1.30 for quad and 1.10 for dual.
Bottom line is if you can afford it quad not only gives you more power punch but also allow you to add more memory later. As max memory size with Quad is 16GB and dual restricts you to 8GB. Just to be future proof I will go with Quad.
One more thing to add is simultaneous thread processing is 4 in dual core and 8 in quad, which does make a difference.