Originally Posted by Imprezzion
Quite simple. CL is purely the amount of clocks it takes to do a certain action. 3000/12 is 250, 4000/16 is also 250. So both actions take the same length of time (8 nanoseconds). This of course ignores all other timings except CL but it's a very rude but correct base calculation. If you cannot get at least CL16 on 4000 it isn't worth it latency wise compared to 3000 CL12.
I'm pretty sure that is for the first bit. On a 64bit system it gets more clear:
MHz CasL ns/cycle first bit 8bits 64 bits
3000 12 0.33 4.00 6.33 25.00
4000 16 0.25 4.00 5.75 19.75