Test Setup

Test System
CPU:	Intel E6300 Allendale 1.8 GHz, 2 MB Cache
Motherboard:	ASUS P5B Deluxe BIOS 0806 Intel P965 C1
Video Card:	ATI Radeon X850 Pro PCI-E
Harddisk:	Maxtor DiamondMax 160GB
Power Supply:	OCZ GameXStream 700W
Software:	Windows XP SP2, Catalyst 6.9

Performance

In the first test we evaluate how these modules do at their default settings of 6-6-6-18, to establish a baseline performance value. A big plus of these modules is that they run at 1.8V without any voltage increase.
Next we tried to determine how the memory handled CL5 and CL4 timings, at lower memory frequencies. If you compare the first three results you can see that changing memory clock, at constant CPU clock, has very little effect on performance.
The next three tests show how well the memory responds to different voltages at the CL6 setting. The frequencies shown are the maximum stable clock at this setting. With only 3 MHz increase per 0.1V of added voltage, the overclocking potential is rather slim.
We see the same picture in the voltage scaling tests at CL5, each 0.1V increase in memory voltage gives you about 3 MHz in overclocking, definitely not worth it.
At CL4 we tested only the maximum overclock at 2.0V, running the modules at CL3 was not possible.

After looking through the benchmarks you can see that maximizing CPU clock is the most important factor when it comes to performance, then you should optimize memory speed.

G.SKILL F2-6400CL6D-4GBMQ 4 GB Kit
CPU Clock & Memory Ratio	Memory Speed	Memory Timings	Everest Read	Everest Write	Everest Latency	Quake 3 Timedemo	3DMark 2001SE	SuperPi Mod 1M
7 x 266 2:3	400 MHz	6-6-6-18 1.8V	6084 MB/s	4803 MB/s	81.6 ns	361.3 fps	26047	29.18 s
7 x 266 4:5	333 MHz	5-5-5-15 1.8V	5797 MB/s	4782 MB/s	79.8 ns	360.3 fps	25911	29.25 s
7 x 266 1:1	266 MHz	4-4-4-12 1.8V	5352 MB/s	4800 MB/s	85.9 ns	359.1 fps	25770	29.43 s
7 x 278 2:3	417 MHz	6-6-6-18 1.8V	6364 MB/s	5023 MB/s	78.0 ns	377.1 fps	26924	27.89 s
7 x 280 2:3	420 MHz	6-6-6-18 1.9V	6412 MB/s	5055 MB/s	77.4 ns	380.2 fps	27007	27.68 s
7 x 282 2:3	423 MHz	6-6-6-18 2.0V	6478 MB/s	5093 MB/s	76.9 ns	381.2 fps	27235	27.48 s
7 x 282 4:5	353 MHz	5-5-5-15 1.8V	6133 MB/s	5044 MB/s	75.3 ns	381.2 fps	27152	27.59 s
7 x 285 4:5	356 MHz	5-5-5-15 1.9V	6204 MB/s	5098 MB/s	74.6 ns	385.8 fps	27507	27.28 s
7 x 287 4:5	358 MHz	5-5-5-15 2.0V	6247 MB/s	5192 MB/s	74.0 ns	388.4 fps	27501	27.09 s
7 x 295 1:1	295 MHz	4-4-4-12 2.0V	5921 MB/s	5323 MB/s	77.8 ns	395.9 fps	27991	26.59 s