The results are obvious. If we divide the PCMark Vantage score by the average power required, we get the efficiency in performance per watt. The best result is reached by the 3.9 GHz setting, which did not require a voltage increase; 3.6 GHz was second, and even 4.26 GHz at increased voltage turns out to provide better efficiency than the 3.33 GHz default setting, which we found surprising. Clearly, Intel’s clock speed strategy doesn’t allow users to fully benefit from the Core 2 Duo’s possible power efficiency—a 3.66 GHz model would be great to have.
We created a little diagram to let you visualize the efficiency at speeds between 3.33 and 4.26 GHz: levels up to ~3.8 GHz at stock voltage seem to be ideal to capitalize on the Core 2 Duo’s performance without excessive increases in power consumption.