Right now 1600/9 is considered the entry level, 1866/9 is better performance (it has a wider bandwidth), faster DRAM is most beneficial if you multi-task at all (i.e. multiple windows), it also improves when doing video, imaging, CAD, VMs, and memory intensive software or using large data sets. Another point for faster DRAM is price, these days 1866 and oftenn even 2133 is right about the same price as 1600 so it makes sense to get faster as more and more software and games are utilizing DRAM more and more