How to downclock my mobile chipset?

[tut]

Environment:
Hardware GeForce Go 6100
OS FreeBSD 7.1-PRERELEASE
X xorg-7.3_2 ('Coolbits' option is set to 1)
Driver nvidia-driver-180.16

$ nvidia-settings -q GPUOverclockingState -q GPU2DClockFreqs -q GPUDefault2DClockFreqs -q GPU3DClockFreqs -q GPUDefault3DClockFreqs -t
1
100,0
100,0
425,0
425,0
Tried to downclock without success - original clock value did not change:
$ for ((i=99;i>=25;i--)); do echo "--> $i"; nvidia-settings -a GPU2DClockFreqs=$i,0 ; nvidia-settings -q GPU2DClockFreqs -t ; done
--> 99

Attribute 'GPU2DClockFreqs' (tut.at.home:0.0) assigned value 99,0.

100,0
--> 98

Attribute 'GPU2DClockFreqs' (tut.at.home:0.0) assigned value 98,0.

100,0
...
--> 26

Attribute 'GPU2DClockFreqs' (tut.at.home:0.0) assigned value 26,0.

100,0
--> 25

Attribute 'GPU2DClockFreqs' (tut.at.home:0.0) assigned value 25,0.

100,0

$ for ((i=424;i>=106;i--)); do echo "--> $i"; nvidia-settings -a GPU3DClockFreqs=$i,0 ; nvidia-settings -q GPU3DClockFreqs -t ; done
--> 424

Attribute 'GPU3DClockFreqs' (tut.at.home:0.0) assigned value 424,0.

425,0
--> 423

Attribute 'GPU3DClockFreqs' (tut.at.home:0.0) assigned value 423,0.

425,0
...
--> 107

Attribute 'GPU3DClockFreqs' (tut.at.home:0.0) assigned value 107,0.

425,0
--> 106

Attribute 'GPU3DClockFreqs' (tut.at.home:0.0) assigned value 106,0.

425,0

Any suggestions?