We did some overclocking with both CPUs. Since they come with their clock multiplier unlocked, you can achieve very high overclocking levels with both of them. In both cases we used a different motherboard, as the boards we were using don’t provide good overclocking options. All the other components were the same, using a GeForce GT 430 video card. We ran Far Cry 2 to test the system stability (i.e., to make sure the system wasn’t crashing).
We used an ASUS Crosshair IV Formula motherboard (1102 BIOS) with the Phenom II X4 975 (3.6 GHz). Without playing with any advanced options, we could increase the clock multiplier of this CPU from 18x to 20x, and increase the base clock up to 206 MHz, making this CPU to run internally at 4.12 GHz. Then we decided to play with voltages a little bit. Increasing the CPU main voltage from 1.4020 V to 1.5375 V made us able to increase the base clock up to 213 MHz, making our CPU to run internally at 4.26 GHz, a good 18.3% overclocking.
To overclock the Core i5-2500K (3.30 GHz) we used an MSI P67A-GD65 motherboard (1.0 BIOS). Without playing with any advanced options, we could increase the clock multiplier of this CPU from x33 to x42, and increase the base clock up to 110 MHz, making this CPU to run internally at 4.62 GHz. Then we decided to play with voltages. We increased the CPU main voltage from 1.208 V to 1.400 V, and we were able to increase the clock multiplier even further to x44, keeping the base clock at 110 MHz. This made our CPU to run stable at 4.84 GHz, a 46.7% increase in the CPU internal clock rate.
It is very important to remember that we got an engineering sample from Intel, which may have a higher overclocking capability than the final product that will arrive on the market.
We didn’t play a lot with all overclocking options, and you may achieve even better results.