Long computer questions?

The Core 2 Quad Q9400 is the best because it has the faster FSB, the most L2 Cache, and highest clock speed with the FSB. the 3/4/6MB means how much cache is there, and the more you have the more you can multitask. Even though the E7400 will have the highest clock speed, it is paired with a more slower FSB so comparing it and the Q9400 at single-core tasks the difference will not be that much.