Hi newcomer and welcome to the Tom's hardware forum.
The CL is in some words, the time that take the data in are available to the processor when the processor need this.
Now, the difference between that two RAMs is that the CMP6GX3M3A1600C8 support XMP. What is XMP?, is an option for Intel rigs to OC the RAM with pre-build settings on the RAM configuration.
Let's say that u buy that RAM, at stock is 8-8-8-24 at 1.65V @ 1600MHz, but when u select the 1st XMP profile the RAM change that setting to 9-9-9-24 at 1.65V @ 2000MHz, that means XPM, OC the RAM.