For our practical experiments we put together the following testbed:
- Mainboard: ASUS P5Q Pro (BIOS 1104);
- Core 2 Extreme QX9650 (3.0GHz, 333MHz FSB, 2 x 6MB, Yorkfield rev. C0);
- Core 2 Duo E8500 (3.33GHz, 333MHz FSB, 6MB, Wolfdale rev. E0);
- CPU cooler: Scythe Mugen (Infinity);
- Memory: 2GB DDR2-1111 SDRAM (Corsair Twin2X2048-8888C4D);
- Graphics card: OCZ GeForce 8800GTX;
- HDD: Western Digital Raptor WD1500AHFD;
- PSU: SilverStone SST-ST85ZF.
All tests were performed in Windows Vista Ultimate x86 SP1 operating system.
First of all we decided to check how well this board overclocks processors. The Intel P45 Express based solutions we tested before coped well with dual-core processors overclocking, but couldn’t succeed when it came to overclocking a quad-core CPU from Core 2 Quad or Core 2 Extreme family. Therefore, we performed a few experiments with different CPUs on our ASUS P5Q Pro trying to reach maximum FSB frequencies.
First of all we installed a Core 2 Dup E8600 processor – a new CPU with a more overclockable E0 processor stepping. Its nominal frequency is 3.33GHz and the multiplier is set at 10x. We managed to reach 4.4GHz with the same multiplier and increased to 1.4V processor Vcore: we only had to push FSB frequency to 440MHz.
Note that all voltages except processor Vcore were left at their defaults. In other words, Core 2 Duo E8600 overclocking on ASUS P5Q Pro required minimal efforts on our part. The system was absolutely stable, according to the Prime95 test and a 1-hour OCCT Perestroika run.
We continued pursuing our goal and undertook another experiment with the same processor but with the multiplier lowered to 8x. Of course, FSB needed to be increased much more dramatically in this case, so finer overclocking techniques had to be applied. The problem here could be increasing the chipset North Bridge voltage, because the chipset cooling system of ASUS P5Q Pro may fail to cope with a much hotter chip. Even replacing the original thermal interface with a more efficient organic silicon thermal compound didn’t help us push the NB voltage over 1.32V. As a result, we couldn’t reach stability at FSB speeds beyond 540MHz. Further MCH voltage increase resulted into chip overheating.
In other words, we achieved the same results with the multiplier lowered to 8x as we did with 10x. The CPU overclocked only to 4.32GHz, which is, actually, pretty good, too.
Note that we had not only to increase the CPU Vcore, but also other voltages to make sure that the processor remains stable at 540MHz FSB. CPU PLL Voltage was set at 1.56V, FSB Termination Voltage was increased to 1.28V. It is important to keep in mind that this FSB frequency is far not the maximum for ASUS P5Q Pro: it is the maximum its default cooling system can handle. Replacing the cooling system with something more efficient will reveal the true overclocking potential of this board and ensure stably system operation at higher FSB speeds.
This result allowed us to check ASUS stability with aggressive memory timings. In above described conditions the memory worked at 1800MHz with 4-4-4-12 timings. Of course, we increased Vdimm to 2.3V.
We have already seen multiple times that Intel P45 Express based mainboards can very well overclock dual-core processors. However, things are not so good when it comes to quad-core processors. ASUS P5Q Pro once again proved that this is indeed the case.
To be more exact, we decided to find out the maximum FSB frequency at which ASUS P5Q Pro can ensure stable work of a quad-core Intel Core 2 Extreme QX9650 processor. We reduced the CPU multiplier to 8x and set CPU PLL Voltage and FSB Termination Voltage at the maximum safe values of 1.7V and 1.35V respectively.
With these settings our processor remained stable at 453MHz FSB.
Of course, this is not the maximum for our processor, however, we couldn’t do any better than that even with significantly higher CPU PLL Voltage and FSB Termination Voltage settings, which would normally have a significant influence on the quad-core CPU overclocking. Even when we increased FSB Termination Voltage to 1.5V, we got stuck at FSB frequencies slightly over 460MHz.
In other words, ASUS P5Q Pro is far not the best platform for quad-core processors overclocking. Solutions on Intel X48 Express seem to be much better cut for this.
Here I would like to add that during our experiments we have once again detected incorrect mainboard behavior in case of over-overclocking. Just like ASUS P5Q3 Deluxe we tested earlier, if P5Q Pro can’t boot with the settings your chose, it will not reboot in safe mode and offer to correct the faulty settings. Instead it will clear CMOS completely and you will have to reconfigure everything all over again in the BIOS Setup.