If your cpu is amd, then it will benefit from faster ram.
Sandy and ivy bridge cpu's have excellent ram controllers that keep the cpu fed with data from any speed ram. . If your cpu is sandy or ivy bridge, then ram faster than 1600 is only marginally helpful.
Here is one report from a year or 2 ago: http://www.anandtech.com/show/4503/sandy-bridge-memory-scaling-choosing-the-best-ddr3
Ram performance is somewhat related to the cas divided by the speed, resulting in almost equal performance from many different combinations.
My take is that more ram is a better value than higher performance ram.