Actually, I do not agree with the comment "at the same price point, the Core i3/i5/i7 will perform better than and C2D/C2Q"
My desktop has an Intel E6300 Dual Core 2.8GHz (overclocked to a 3.1GHz). Even without overclocking, it out does any i3 and almost any 2-core i5.
Just like you pay more for Alienware as a "Brand Name", you pay more for Core iX series processors because you pay for "Brand Name".
-Klosteral