Force video frequency to 50Hz-> 11 sp2

Dear all,
I am trying to drive my 2 monitors in extended desktop with the resolution of 1920x1200 [60Hz]-each-
OS is SLED 11 SP2, kernel 3.0.13-0.27
I am getting some synchronization problem (the monitor are flickering), and I would like to decrease the refresh frequency to 50Hz to check how it is working.
I tried to modify xorg.conf but I am not able to get any result (the refresh frequency is always 60Hz).
I tried to work with sax2 but the frequency cannot be lowered below 60Hz.

Can you please help me?

Thanks in advance

PS: as you can see I am not a master of Linux :frowning:

What graphics card are you running? Also can you post the output from the xrandr command;

/usr/sbin/hwinfo --gfxcard