About PowerMizerLevel: Is it related to CUDA performance?

i found there are three levels in the nvida control pannel.

Is it related to CUDA’s performance?

Can I get the best performance through setting it to the highest level?

Another question is How to set it?

In my computer I have two GTX295 card, this means total 4 GPUs.

I added two lines into the section “Device” of xorg.conf as following

BusID "PCI:5:0:0"

Option "RegistryDwords" "PowerMizerlevel=0x1"

and rebooted the computer, but the level is still the lowest one.

Who know how to set it?

btw, the PCIbus for 4 GPUs are

device #0 : PCI:5:0:0

device #1 : PCI:4:0:0

device #2 : PCI:8:0:0

device #3 : PCI:9:0:0

Why 5 is before 4?

Thank you.