One thing that needs to be explored is the full range of power specifications. One trick that intel likes to pull with their lower powered CPUs, are alternate TDP ranges where a 15 watt TDP is set as a default but they may add an alternative power limit that the CPU can use if the thermal headroom is available.
For example, on some of the really low powered Intel CPUs targeted at tablets and ultrabooks, you may see a CPU with a factory default package power limit of 11 watts, and a and an alternative power limit that is used if thermal headroom is available for 15 watts. And tablet makers looking to get away with very little cooling, will set a power limit of 6 watts or less, thus causing the CPU to not even reach its base speed if the integrated GPU enters its 3D acceleration mode, since the package will TDP throttle.
Intel will then push out newer generations where they up the boost clock, and then up the alternate power limits, and then claim massive performance improvements, but when implemented in the real world, those benefits disappear because people realize that they only last for about 30 seconds before the system throttles.