wiedehopf

If the aim is to run some Intel processors as efficient as possible, changing the power limit won't necessarily get it into the efficient frequency for single core loads.

For that it's necessary to set a maximum turbo frequency, this can be done like this:
for freq in /sys/devices/system/cpu/cpufreq/*/scaling_max_freq; do echo 3000000 > $freq; cat $freq; done

The default for N100 is 3.4 GHz which it will only boost to for a single core.
The following testing was done at PL1/PL2 at 15W. (i wouldn't recommend lowering PL1/PL2 below 14 W for efficiency unless you have issues with cooling)
Single core wall power draw for `stress-ng -c 1` stressing a single core:

max_freq    pWallSingle     geeks   geekm       geekl