Thank you Lawrence.
It would be interesting if you could add the difference between CPU and VRM temperatures with the stock heatsinks for comparison. Intel makes a big deal of the need for airflow on the VRM area but we have no reference for what that means in terms of the reported VRM temperature value.
why, if Sandy Bridge is so efficient, the CPU temperatures are so worse than the previous ones
(15-25°C more, with reference to the Athlon II X4 platform)?
It *is* more efficient, by a large margin.
We don't know the actual temperatures, only what the CPU reports.
Even the actual CPU temperature is not very interesting. The board is the part which is most at risk of overheating with these heatsinks, which is why the reported VRM temperatures are so useful. This gives us real data on which heatsinks are the most dangerous at low fan speeds.
Any difference between actual CPU temperatures is easily explained. Assuming the same heatsink and the same power consumption, the CPU temperature will be mostly determined by the heat transfer between the parts of the CPU which heat up and the contact with the heatsink. If that heat transfer is relatively inefficient, the CPU temperature will be higher.
It stands to reason that a smaller manufacturing process will cause the heat transfer to be less efficient.
Also, a manufacturer of efficient and heat-resilient CPUs would have less incentive to optimize the heat transfer because it's less of an issue with its products than with the products of its competitors. Overclockers might be frustrated by the inefficient heat transfer however...