Tom's Hardware: "The new Thuban-based six-core Phenom II X6 processor is available in two different flavors: 2.8 GHz and 3.2 GHz. Both come with the new Turbo CORE feature that dynamically increases the clock rate of up to three cores. However, the Phenom II X6 doesn’t necessarily run at maximum efficiency when it's operated at stock speeds. In fact, a reasonable overclock provides a solid increase in performance per watt.
Today we determine the ideal clock speed and look at the maximum overclocking speeds using air cooling, because this is where you want justification for spending those extra dollars compared to quad-core processors."