Due to their complex manufacturing process, even CPUs
of the same model and batch can have notable differences in quality.
While defective CPUs are discarded and inferior ones are rebadged, there is still a quality
difference in those that make it past factory inspections.
Getting a high quality CPU from a store is a matter of luck (which is why overclockers get so excited when they chance upon a CPU of exceptional quality). All things being equal, a high quality CPU will run cooler and overclock better than a typical sample.