Perhaps this is already known but I found out that setting DRAM to Raw MHz effectively halved my memory bandwidth. Only discovered it because my 3dmark11 physics score was too low on that setting.

On a related note, this set of GSkill Ripjaws DDR3-2000 9-9-9-27 from my X58 rig is rocking at 2333MHz! Am going to see how far I can push it; pretty cool for a set that's two years old.