1866MHz CL8 or 1866MHz CL9 or 1866MHz CL10?

[Dr Who]

Well there is a promotion in my country on RAM, so i want to buy two sticks of 4 GB each. The question is what Cas Latency should i get? I know CL 8>9>10... but then people said something about frequency and i got so so confused.
PS: All the memory is at 1866MHz.

 

[guggi4]

lower cl at the same speed = better

 

[Dr Who]

Thanks!