Any reason why I should buy kitted RAM vs. regular OEM sticks if I don't plan of OC the RAM?

And one more Q: The difference between CL7 and CL7 DDR3 1600 here is like 30% in price (cca 75$ more). How much of an actual real life system performance do you guys think we shall get from choosing CL7 over the cheaper CL9 memory?