You will see no real gains in-game using faster RAM.
Toms Hardware did an article a while ago showing less than 1% difference between slower RAM, Faster RAM, and higher clocks.
My recommendation for ANY new Core-i7 system is to just purchase the 1.5V 12GB RAM kit from Corsair. It is 1066, but it runs perfectly and is stable with zero risk to your processor.
While Intel recommends nothing passed 1.65V, I do not recommend anything beyond the 1.5V to protect the on-dye memory controller.
What is the point of making a fast system if it doesn't last.