Edit your xorg.conf and change (add one line) the following:
Code:
Section "Device"
[...]
Option "Coolbits" "1"
[...]
EndSection
Then use
nvidia-settings to change your clockfrequencies. That should do the job. Read here for more information about how to make the changes last when you restart etc.:
http://us.download.nvidia.com/freebs...hapter-05.html