which values are best for underclocking 3x6990?

[Jessi]

I have a typical rig (3x6990, MSI 890FXA-GD70, Corsair Professional Series Gold AX1200, Coolmaster HAF-X RC-942, Sempron 140). The overclock-switches of the 6990 are still in their default position.
I am mining with LinuxCoin 2.1 final (ATI 11.6).

Now I am searching for the best values which I can enter for gpu-overclocking and mem-underclocking and a typical value for the fans.
Because I am not very experienced I am searching for some help. I did search this forum allready but I did find many values in different configurations, but no final solution.
To prevent making fatal error, I try it now with this thread. - I am sure someone has done it allready with a simmilar configuration and can help me.

Anyone?

Thank you!!!