how to set logverbose=6 to X server (forever)

[Frédéric Bron]

I have a lot of problems with the nvidia proprietary driver. However
nouveau is very much too slow so that I have to use the nvidia driver.
They ask for logverbose option to be set to at least 6 to send bug
reports. I see how I can do that for a manual start with startx, how
can I do it for all normal starts? I am using F18 with KDE. I do not
want to restart the X server manually each time I switch on the
computer.

Regards,

Frédéric