do Pentium4 & PentiumM consume about the same at their lowest possible freq?

[Roberto De Leo <deleo@unica.it>]

Hi all,
I am not sure this is the right place where posing my question, if not 
please suggest me a better one!

I come to the question.
I happily used the speedstep kernel module with my centrino laptop and 
it really made a difference in terms of battery duration (actually now I 
have a celeron-m based laptop and the difference does not seem so 
evident, but I still have little statistic on it).
Now I need to replace my main home 'desktop' PC and I am tempted to buy 
a PentiumM-based minit-itx MB (e.g. the AOpen i945GTt-VFA) in order to 
decrease the power bill (my PC is on 24/7), but since mini-itx MBs are 
quite expensive I'd prefer first to know the following: can the  "Intel 
Pentium 4 clock modulation" kernel module (or maybe the "AMD 
Opteron/Athlon64 PowerNow!" one) bring the corresponding CPUs to consume 
as little as the "Intel Enhanced SpeedStep" does for a centrino? This 
info is quite important but I could not find it anywhere!

Thanks,
 Roberto