Not much of a question really what are you planing on applying the system to?
For gaming unless your running a APU then the gain from Cas 8 to Cas 9 or 1600mhz to 2000mhz ram really isn't that huge... 1-2%. On non APU's I grab 1600mhz ram and just O.C unless you can find a good deal on Cas 8 2000mhz...good luck with that though. For gaming as well running FX 8 or 6 core again isn't much of a difference as gaming still doesn't use the full potential of having more than 4 cores. If you O.C heavily then you end up shutting down cores regardless.
1600 will suffice for gaming, but as mentioned above there is no gain going from CL8 to CL9, actually it's a loss, you want lower CL not higher. Look for 1600 with CL9 at a minimum (it's entry level for today's systems. The GSkill Snipers and Ripjaws X lines are my favorites for AMD rigs