Not necessarily, Zackon.
With two separate CPUs, you introduce another variable. Namely, the bus or medium by which the two chips communicate. an Octocore chip is going to be better than two quads, because there's barely any latency between the cores. The combined latency between the two CPUs and between the CPUs and RAM would probably cripple it compared to modern multi-core chips. dual-chip setups are mostly used in servers; because unlike normal PCs - a Server has to deliver alot of resources to alot of people reasonably quickly, rather than a few resources to one person instantly. In this case, the latency between them is negligible especially over a network. The only consumer PC currently available that uses dual-chips is the Mac Pro, which is primarily for processing-power intensive activities like video editing, where the chips can both be fully optomised.
Long story short, the signals travelling between two seperate CPUs, and RAM and a GPU or two, would create such a noticeable drop in performance compared to a larger multicore chip in the same situation that it's rarely worth the effort. Besides, Most boards that support dual-CPUs aren't gaming boards, and tend to also only support technologies like ECC RAM and Mirroring (for protection rather than power).