When I am shopping for ram should I be looking at a lower CAS or higher speed? What does a low CAS mean if it is a lower speed- does it make it as fast as a faster clocked ram with a higher CAS?
The speed means very little. FPS levels have been recorded at a maximum of 2 fps change between 2100 and 1333, don't spend more on speed. I recommend 1600.
In regard to your question, I don't know.
If you take the CAS latency and divide it by the speed, it will give an indication.
CAS 9 / 1600 = 0.0056
Cas 11 / 2133 = 0.0051
I actually have some CAS 7 1600
So that would be 7 / 1600 = 0.0043 which makes it faster than CAS 11 2133.
But CAS 9 / 2133 = 0.0042 which makes it slightly faster.
I would advise going with 1600 for all your needs, and then just get the lowest CAS possible. Editing benefits from lower CAS. And the only thing to benefit from higher clocked RAM is an APU. But for a gaming system with a dedicated graphics card, C9 1600 is all you really need.