1600MHz is not required for OCing, it is only really required for EXTREME OCing. I would recommend getting 1600MHz, as it is not much more expensive, if you didn't have the old stick already but it is a waste as you already have it.
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I'm unsure on how AMD systems work but this is how my i3 works. The default base clock is 133MHz, the memory has a default multiplier of 10 (10x133=1333MHz) and the processor has 22 (22x133=2.93GHz). Now if I increase the base clock to OC the processor the RAM will raise above 1333MHz which would eventually loose me stablility. Though the memory multiplier is variable with the lowest setting possible being 6.
So to OC the processor with 1333MHz RAM I lower the memory multi to 6 or 8 so that the memory doesn't get OCed. Now when you need 1600MHz RAM is when you have the memory multi at 6 yet if you increase the base clock anymore it will go over it.
Are you following so far?
Now to figure out when this point of having to have 1600MHz RAM occurs. 1333/6=222. This is the max base clock I am able to reach without pushing the RAM past its spec. But at what processor speed is this base clock needed? 222x22=4.9GHz.
Also you talked about getting a 955 BE. These are called "Black Edition" for a reason, it would in the above example allow me to change the CPU multiplier above 22x and leave the base clock at 133. Therefore NO need for 1600MHz RAM even past 4.9GHz.
Conclusion to the discussion:
For my 1333MHz RAM to become a limit to my OC I would need to reach a processor speed of 4.9GHz. If you haven't noticed this is a very high speed

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So I'm not saying its the same for AMD but I'm sure its similar (don't quote me on that
😀), you will run out of cooling, bravery or gain some sense before the 1333MHz limits you.
Hope you understand that. Note that I wrote all that so that you would learn some stuff not just to show you that 1600MHz was not needed, I could of done that in 3 lines.