I think you are confusing CPU speed (2.4 gHz) with RAM speed (1.6 gHz or 1600 mHz).

Though they are both on the motherboard, the CPU and RAM are entirely different things (though they work as a team a lot).
A given motherboard can often use multiple RAM speeds and the manual usually shows you the range.
If you want ultimate performance, the fastest RAM your motherboard can support would be the optimal choice. However, it's one of those things you can pay a lot more for and get no real noticeable ROI in every day use. (Note that you also need other supporting things to even really use these higher speeds efficiently, like Cas Latency)
FWIW, I think 1600 is the top RAM frequency for the board on this machine also. I think I opted for slower RAM and more of it, but again make sure your total expected number of RAM sticks physically fits into the computer.

If RAM is indeed an issue you'll likely see much more performance increase by simply doubling it (even at the same speed), than if you doubled it and then added the faster RAM aspect.. the faster RAM difference would likely be negligible.

I do not work here, but the benefits are still awesome
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