On ASUS P5B Premium Vista Edition we could find some overclocking options (0402 BIOS):

• FSB clock: Can be adjusted from 100 to 650 MHz in 1 MHz steps.
• PCI Express clock: Can be adjusted as auto or from 90 MHz to 150 MHz in 1 MHz steps.
• CPU voltage: auto or from 1.1000 V to 1.7000 V in 0.0125 V increments.
• Memory voltage: auto or 1.80 V to 2.45 V in 0.05 V increments.
• FSB voltage: auto or 1.2 V, 1.3 V, 1.4 V or 1.45 V.
• North bridge voltage: auto or 1.25 V, 1.45 V, 1.55 V or 1.65 V.
• South bridge voltage: auto or from 1.5 V to 1.8 V in 0.1 V increments.
• South bridge I/O voltage: auto, 1.057 V or 1.215 V.

This motherboard also provides several memory timings adjustments, as you can see in Figure 17.

click to enlarge
Figure 17: Memory timings adjustments.

On this motherboard there is no way to lock the memory clock at a specific clock rate, so overclocking the CPU you will automatically overclock the memory as well. This may be a problem as the maximum clock your memories can achieve may limit your overclocking. On the other hand, you can configure the FSB/memory clock ratio, so you may increase this when you think your memories are running at a too high clock.

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.

The maximum external clock rate we could configure on this motherboard was 323 MHz. With this overclocking our Core 2 Duo E6700, which normally runs at 2.66 MHz, was running at 3.23 GHz, an impressive 21.42% increase on its internal clock rate. With this overclocking our system performance increased 21.65% on Quake 4 and 13% on PCMark05.

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.

Just for reference, on ASUS P5N-E SLU we could set our CPU running at 327 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 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.