Quad Core, 8MB L2 cache => 2MB L2 cache/core
Dual Core, 6MB L2 cache => 3MB L2 cache/core
I'm a student at the Automation and Computer Science Faculty in the Technical University of Cluj-Napoca, Romania, 4th year of studies... so I studied how this things work (down to tranzistor scale).. and I must say.. 1MB L2 cache is making a very big difference... I would say to go with the Dual Core..
L2 cache is the fastest memory in a PC.. L2 cahe is with RAM like RAM with HDD
L2 is that fast because is on the Core chip, and it's communicating with the CPU directly.. hope I made myself clear, I didn't had to explain this before to anyone
Plus that, as Thomas mentioned, very few programs are optimized to use 4 cores. I'm positive that 2 cores with more L2 cache will make a better job than 4 with less L2 cache.. I'm a programmer too
and the multi-thread programming is a nasty "pain in the ass"