TweakTown posted a review on the Kingston HyperX PC3-17066 (2133MHz) 4GB Kit

Kingston has a reputation for creating some extremely high quality memory. What this means is that we tend not to see the company jump on the speed train as quick as some other makers do. They want to know when they release a module that it's going to run 100% across many platforms.

Due to the nature of this, what tends to happen is we see only major step-ups in speed. To give you a better idea from Kingston, we see at the top of the table the 2133MHz DDR kit we have with us today. Moving downwards and we've got 2000MHz which was a major release, while below that there are 1800MHz DDR, 1600MHz DDR and 1333MHz DDR modules.

Kingston HyperX PC3-17066 (2133MHz) 4GB Kit Review