Summary And Conclusions: Spare Yourself Of CL 1.5
The only real consequence of using the GeIL DIMMs at CL1.5 timings is the need to boost input voltage to at least 2.9V. Beyond that, this faster mode of operation works inconspicuously. So inconspicuously, in fact, that we had to double-check to make sure our configuration really included the correct timing parameter. Nor could we really prove to our own satisfaction that this parameter was in effect, and thus had to rely on the setting shown in the BIOS and verified by CPU-Z. That's why we suspect that the Athlon 64 barely supports this short CAS latency setting, nor appears to be able to make any effective use of it, either.
Our test system delivered a pleasant surprise, however. We hadn't tackled any serious overclocking projects for some time, so a jump from 200 to 300 MHz in the system and memory clocks gave us legitimate cause for concern. But no "Hail Marys" were needed, because all of our components - including the DFI LANParty nF4 Ultra-D, the Athlon 64 4000+ with Clawhammer core, and the GeIL memory modules - gave us no grief whatsoever. In fact, everything went without a hitch!
At DDR600 clock rates measurable performance improvements may be possible, but primarily for memory dependent applications like WinRAR. Gamers don't appear to benefit much, if at all. And while other applications might benefit from higher clock rates, they may also lose as much as they gain from slower timings recommended for DDR600.
Our conclusions offer no fundamental changes to anyone's worldview: Stable, fast memory with the shortest possible timings still represents a form of unattainable perfection. Those willing to venture into overclocking territory may realize higher performance by continually pushing that envelope, but that depends strongly on the applications they use. At least GeIL's lifetime exchange warranty removes the sting of shortened memory lifetimes that overclocking can inflict. But it does nothing to soothe the effects of diminishing returns: this stuff costs the world, but delivers something less than that!