Hello.
Look into your Xorg.log. Maybe your cards pixel clock is the limit there (tho I don't think so actually)
Doesn't matter if the monitors support it if your video device doesn't.
However, as I said, I don't think this is it.
Just go to your ccsm -> general options --> display settings
and disable "detect refresh rate".
I posted some troubleshooting
HERE
*edit*
This thread is 2 years old. You bet nvidia would have long released a fix if it was related to the Powermizer.
However, you can give it a try. You don't need any additional scripts neither, PowerMizer may be configured inside your xorg.conf too. Just read the manual nvidia provides (which is VERY informative actually)
ftp://download.nvidia.com/XFree86/Li....18.14/README/
You could try and enable CoolBits for troubleshooting purpose too... No need to state that you'd do this at your own risk I think.