I use powersave capping the max freq unless I have something big to compile etc (just to help make sure the fans won't kick in, in my case, but it might help)
Just write whatever frequency you want to /sys/devices/system/cpu/cpu[0-9]*/cpufreq/scaling_max_freq and scaling_min_freq
The lowest I can set it to seems to be 40000. I can still hear noise, depending on what the laptop does.
As simple command to create noise is:
while true; do echo -n $RANDOM; done
I guess I would lose about 90% of performance if I permantently set scaling_max_freq to 40000?
I normally scale down to about 1GHz without much visible performance impact except for compiling, and that is enough for fan to not kick in randomly everytime a web page has some somewhat heavy js or whatever it is I'm doing, but obviously you're looking at a different beast.