CL4 vs CL6 for gaming (worth it?)

Hi,

I want to upgrade my ram from 4 to 8gb. I'm looking at a CL6 set for about $90, or a CL4 set for $140. This upgrade is primarily for games. Will I notice any real difference for games between the two?


http://www.amazon.com/Crucial-PC2-6400-240-Pin-Desktop-...
CL=6


http://www.amazon.com/Kingston-Modules-Desktop-KHX6400D...
CL4 (4-4-4-12)


This is my current ram. My second question is, should I just buy one set of 4gb, and see if it works with my current ram before I purchase more?
http://www.ocztechnology.com/ocz-ddr2-pc2-6400-reaper-c...
4-4-4-15