I've been looking at buying a new computer lately, and I'm wondering if I should go with a Dual-core processor or a quad-core. If I take a look at, for example, System76, they have a Core i5-520M Processor with 2 cores and a clock speed of 2.40GHz, and also a Core i7-720QM Processor with 4 cores and a clock speed of 1.60GHz.
So the one with 2 cores has a higher clock-speed and the one with 4 cores has lower clock speed. So which way should I go with this tradeoff, and why? Is the clock speed more important to a high performance system, or the extra cores?