@brumby 1990 I dont think so, ive never heard of that. PCIe overclock can greatly UNSTABALIZE your system. Especially since USB 3 + Gfx cards + Sata are on that bus. I always lock @ 100mhz instead of leaving it on Auto just in case.
@Impunity, 6 or 7 @ 1600 is normally reserved for high end kits. 8 for midrange, 9 for lower end. Whats the brand/model of the ram? If it started out as a low end kit, you could probably expect it to tighten to CL9 easy, if its decent corsair/gskill/mushkin you could get even lower.
CAS latency is pretty much the minimum amount of time to access a random memory address and have its data available. Although im not 100% why, its always been the faster you push your ram, the harder it is to maintain the low latency. http://en.wikipedia.org/wiki/CAS_latency
for more reading.
In general, the lower the CAS latency, the better. Because modern DRAM modules' CAS latencies are specified in clock ticks instead of time, when comparing latencies at different clock speeds, latencies must be translated into actual times to make a fair comparison; a higher numerical CAS latency may still be a shorter real-time latency if the clock is faster. However, it is important to note that the manufacturer-specified CAS latency typically assumes the specified clock rate, so underclocking a memory module may also allow for a lower CAS latency to be set.
--Edited by kevinf - 8/21/11 at 6:03pm