I have to say that the numbering/labeling conventions for memory are really confusing.
I talked to Crucial for a while today and they suggested buying the 1333-level sticks and leaving the voltage lower. I don't know if I'd be lowering it as an active step or just letting the board set the voltages by itself. (Gigabyte GA-X58A-3UR) 3 sticks x 2GB. I will not be gaming; I am building this for Photoshop work. Having 6Gig, a 64-bit OS, GPU acceleration, and a really fast processor will be an amazing uptick in productivity so I feel that the little bump I'd get from tweaking RAM at this level of detail would not pay itself back after time invested in learning, experimenting, trying different solutions.
My 2 cents.