The description of the mainboard’s BIOS Setup shows that the ASUS P5N-E SLI is not as settings-rich as many other overclocker-friendly mainboards are, but it does allow to change all the main parameters. Hopefully, it can make a good platform for overclocking, too.
Furthermore, mainboards for power users that we have discussed lately on our site have very sophisticated BIOS Setup programs you can spend hours in, trying to find optimal settings. The ASUS P5N-E SLI is a relief in this respect. It offers two frequencies and three voltages, just what you need to overclock your CPU. Of course, you can hardly hope to set any overclocking records with such scanty settings, but anyway.
To check out the mainboard at overclocking, we took an Intel Core 2 Extreme X6800 processor, 2GB of DDR2 SDRAM (Corsair TWIN2X2048-8500C5D), a PowerColor X1900 XTX 512MB graphics card, and a Western Digital Raptor WD1500AHFD hard disk drive. Using the mainboard’s quasi-asynchronous memory mode, we made the memory modules work at a frequency of 800MHz or a little lower with 4-4-4-12-1T timings throughout our tests. The CPU was cooled with a Zalman CNPS-9500LED cooler and we also installed a 60mm fan on the North Bridge heatsink. The stability of the system was verified by running the ORTHOS program, which was based on Prime95 code.
We soon found the highest FSB frequency the mainboard was stable at. Just like in our tests of the ASUS Striker Extreme, it was 490MHz.
To achieve this result we had to increase the North Bridge voltage to 1.563V and the CPU voltage to 1.475V. It seems simple, but it is not. It’s been a long time since ASUS made its last mainboard on which all overclocking options worked well without any reservations.
First, we achieved such a high FSB frequency only after installing a fan on the North Bridge heatsink. Without that fan, the mainboard would freeze during the POST even at 450MHz FSB.
Second, tests suggest that there’s little sense in high FSB frequencies on the ASUS P5N-E SLI as well as on the ASUS Striker Extreme. The FSB strap is changed somewhere within the 400-450MHz range and leads to a catastrophic hit of memory performance, which is not always made up for well by the CPU frequency growth.
Third, we encountered a FSB hole with our ASUS P5N-E SLI. The mainboard was totally inoperable at FSB frequencies from 400 to 450MHz.
Besides that, the P5N-E SLI sets the voltages too low, which is typical of ASUS mainboards. Particularly, the real CPU voltage proves to be about 0.05V lower than the value you set in BIOS Setup. It also bottoms out by about 0.05V more at high CPU loads, which is within the Intel specifications, but irritates overclockers.
The quasi-asynchronous clocking of memory by the nForce 650i SLI chipset allows overclocking DDR2 SDRAM independently from the FSB on the discussed mainboard. We tried to find the highest frequency for our TWIN2X2048-8500C5D modules at 2.4V voltage, but were somewhat disappointed. The ASUS P5N-E SLI proved to overclock DDR2 SDRAM worse than the Striker Extreme had done. The maximum memory frequency we achieved was 550MHz.
On the ASUS Striker Extreme these very modules had worked at 587MHz. Still, we have some hope for improvements in the future versions of the mainboard’s BIOS. We used version 0401 which was already much better in that respect than the previous versions, indicating that ASUS was still working on the mainboard.