I think it ought to be mentioned that Zalman got their start producing products for PC enthusiasts who sought to reduce the noise produced by their computer. Their priority is silent operation, not the lowest possible temperatures, which is the expectation of overclockers. It's no surprise to me that the Zalman CNPS8000 allowed the overclocked E6300 at 3.06GHz to rise to 80 degrees C. After all, it's only a 92mm fan, and with the Fan Mate controller set to its lowest speed, the fan was receiving just under 5 volts*. If you intend to overclock with this heatsink (especially the hefty 60% overclock being run on the E6300 in testing), run the fan at its highest speed. However, please remember that overclocking is not the target market for the CNPS8000. Instead, the intended usage is noise reduction of components being run at their stock speed.
That said, even with its intended application in mind, the CNPS8000 isn't that great of a cooler anyhow. Even with the E6300 running at its stock speed, with the fan on its low speed**, I'd hope for better results than the measured average temperature of 66 degrees, though I'm not rushing in with a bucket of water quite yet. The Fan Mate controller is infinitely variable between 5V and 10.5V, so there's a wide range of adjustment available, allowing a user to select the speed that provides the best balance of cooling and low noise. Another site, Silent PC Review, comments that the fins on the CNPS8000 are closely-spaced, which decreases the heatsink's efficiency when there is little airflow. Of course, the idea here is that the CNPS8000 was to round out the product line with a low profile solution using heatpipes, though sadly it still performs only about as well as heatsinks using an extruded aluminum fin structure with no heatpipes. I think this CPU cooler would still be a useful cooler for home theater PC applications, where gaming performance isn't at issue (so overclocking would be of little value), and where low noise is desired, though it isn't a good value at all. I think it's unfair, however, to expect the same results as you'd get with the much larger CNPS9500 and CNPS9700 coolers.
One thing that could have improved the CNPS8000's performance would be if they had used a "swaging" process to sink the aluminum fins into slots in the copper base at the bottom. Also, at either end of the fin structure, there are some fins that are slightly more than half the width of the rest of the fins. These should probably have been made full-width instead of half-width. This type of fan blade generally moves most of its air in a cone-shaped pattern away from its hub, rather than directly along the shaft's axis, so the fan design used here probably allows much of its air to be directed through the low-pressure regions at the corners of the fan housing, where there are no fins.
*Determined in my own testing of a Zalman Fan Mate 1 controller.
**Assumed, given the measured thermal performance.
