Embarassingly simplistic and ultimately stupid. Most of Penryn's die is cache which is not remotely hot as the cores so getting rid of it will not get you to a quarter of the power as witnessed by 3MB models which occupy the same power slots as the 6MB models. AMD is actually increasing the cache size on their next mobile model while decreasing power. Silverthorne only has 0.5 MB of cache which means the core is a greater percentage of its die size and should be closer in power to Penryn if it was actually related which it isn't.