no, good DDR3 1600 usually has a CL of 7, like the G.Skills nos has, or OCZ Golds...
i believe the main limitation for overclocking RAM is the slight oscillations on voltage which occur over read and write cycles of a given memory bank... as the timings decrease, the frequency of the voltage oscillations increases, which causes instability in the link to the CPU (be it directly or through the FSB)...
because DDR3 has lower voltages, the amplitude of the oscillation as a portion of the total voltage becomes greater at looser timings, which causes instability at higher threshold timings for any given DRAM frequency... it is mainly for this reason that tighter timings can be achieved at higher voltages...
regardless of this, the incredible bandwidth offered by the triple channel nature of DDR3 negates the small loss due to looser timings