from http://wiki.maemo.org/Overclocking

setting the lowest frequency to 125 MHz does NOT improve battery life. In fact, many people noticed worse battery life, instability and worse responsiveness

in fact, it actually extends the time between processor goes from 250Mhz to 0Mhz (sleep)

anyway, if you look at the chart, you'll notice that 125 and 250 consumes the same voltage in ULV XLV and Ideal

also from:

http://wiki.maemo.org/Kernel_Power#Remarks

if you enable 125MHz also set "echo 1 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice_load"

there are several clock freqs that are avoided, you have to edit

/sys/devices/system/cpu/cpu0/cpufreq/ondemand/avoid_frequencies