Because of the heterogeneity of the different CPU designs, each class of CPU has its own requirement for HSF testing. Everyone uses different testing criteria and methods, ranging from a calibrated heat source to simply running the test system in idle and load and reporting the temperature values as displayed by the mainboard's hardware monitor. To say it upfront, there is no perfect way of measuring the efficacy of any heatsink and there are no perfect guidelines either. All these parameters have been thoroughly analyzed and can be used to calculate the performance of an optimal HSF for a first pass design. Still, there are a few rules of thumb.
Copper is somewhat twice as good as aluminum.
Doubling the height of the fins is equivalent to a 4-fold increase in fan power. Thickness of the base plate is negligible in terms of overall performance. All of these parameters and guidelines need to take into account that, beyond a certain point, the returns are diminishing. Even though the above explanations are quite intuitive, there are a few points that are, at least surprising. Needless to say that the average person would not think about a fan running twice as fast to be 32 times louder.