On ASUS P5N-E SLI we could find several overclocking options (0602 BIOS):

• FSB clock: Can be adjusted from 533 to 3000 MHz in 1 MHz steps. As the clock here isn’t the real clock but the QDR clock (i.e., four times the real clock), this means that you can adjust the external clock rate from 133 MHz to 750 MHz in 0.25 MHz steps.
• Memory clock: Can be adjusted from 400 to 2600 MHz in 1 MHz. As the clock here isn’t the real clock but the DDR clock (i.e., two times the real clock), this means that you can adjust the memory clock rate from 200 MHz to 1,300 MHz in 0.5 MHz steps.
• PCI Express clock: Can be adjusted as auto or from 100 MHz to 131 MHz in 1 MHz steps.
• CPU voltage: auto or from 0.83125 V to 1.60000 V in 0.00625 V increments plus a 100 mV (0.1 V) offset that can be added on top of this configuration.
• Memory voltage: auto or 1.920 V, 2.013 V, 2.085 V, 2.178 V, 2.259 V, 2.353 V, 2.454 V or 2.517 V.
• North bridge voltage (SPP): auto or 1.208 V, 1.393 V, 1.563 V or 1.748 V.

This motherboard also provides several memory timings adjustments.

This motherboard provides some important overclocking features not found on other mainstream motherboards and even on some high-end models.

The most important one is the ability to lock and configure the memory clock independently from the CPU external clock. On almost all motherboards the memory clock is derived from the CPU external clock, so if when you overclock the CPU you automatically overclock the memory as well. Thus when you reach the maximum overclocking your system can take you will never know what is limiting your computer from reaching an even higher overclocking, the CPU or the memories. With this option you can lock your memory clock at their standard clock rate (e.g., 800 MHz) and only after you found the maximum clock rate your CPU can take you may start increasing the memory clock rate in order to find the maximum clock rate your memories can achieve.

The PCI Express clock configuration is also very important, as you can lock the PCI Express clock at a given value (100 MHz, for example). Usually when you increase the FSB clock you will automatically increase the PCI Express clock as well, and sometimes your overclocking will be limited not by the CPU but by the devices connected to the PCI Express bus. Thus with this option you can increase the probability of setting a higher overclocking.

On this motherboard the external clock rate is configurable at 0.25 MHz steps and a lot of people may not notice this, because in the setup the FSB clock rate is referred by its quadruplicated value (QDR), not by the real clock rate like on almost all other motherboards.

For instance, the maximum external clock rate we could configure was 1,308 MHz (i.e., 327 MHz), with our memories locked at 800 MHz. With this overclocking our Core 2 Duo E6700, which normally runs at 2.66 MHz, was running at 3.27 GHz, an amazing 23% increase on its internal clock rate. With this overclocking our system performance increased 10.65% on Quake 4 and 12.55% on PCMark05.

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Figure 6: Maximum overclocking with ASUS P5N-E SLI.

We could configure our external clock above that but the system was unstable. We only consider our overclocking to be successful after we can run at least four times Quake 4 and PCMark05 with no errors.

We don’t know the magic ASUS did on this motherboard, but with P5N-E SLI we could achieve the best overclocking from all socket 775 motherboards we reviewed to date – on ASUS P5B Premium we could set our CPU running at 323 MHz, on ASUS P5B we could set our CPU running at 316 MHz, on MSI P35 Neo Combo we could set our CPU running at 314 MHz, on ECS NF650iSLIT-A we could set our CPU running at 308 MHz and on ECS PN2 SLI2+ we could set our CPU running at 306 MHz.

We, however, didn’t play with voltage settings or any other fancy adjustments, so you may achieve a better overclocking than we did with more time and patience – on this motherboard and also on the other motherboards we reviewed.