if you hav cas3 memory it is better to force it to use cas2. Only with top quality memory like crucial, micron, infineon, etc cas2 should you set it at SPD because then it will choose the best settings for you like interleaving and what not. If you don't have that memory get the OC'ers bios and force interleaving and cas2.
I have 256mb crucial cas2-2-2 so that's why i get the really good memory scores when i have it set to SPD