The CMX12GX3M3A2000C9 is crap - don't use them. I use the CMT12GX3M3A2000C9 and they're great.
It depends on what the 'use' of your PC; for 'Gaming' sure the DDR3-2000 adds a few FPS but they're not for the newbie because they require you to OC at minimum the BCLK to 160MHz or higher.
The CMP24GX3M6A1600C9 are fine, the CMZ24GX3M6A1600C9 is cheaper and performs the same, and you might want to see this video -> http://www.youtube.com/watch?v=5AOylHaCyUA
or remember Memory Configuration Protect -> Enable.