Overclocking greatly varies due to what hardware is being used and who is doing the overclocking. Always remember that no two pieces of hardware will perform the same, so our results will differ from what you might be able to get.
Remember that the stock speed of this Black Edition CPU is 3.6 GHz with a multiplier of x18 and a 200 MHz bus speed.
Since the Phenom II X4 975 is a Black Edition processor, the multiplier is unlocked. We were able to change the multiplier from x18 to x20 while also increasing the bus speed from 200 MHz to 220 MHz to obtain an effective 4.4 GHz overclock. This is 800 MHz higher than the stock speed of 3.6 GHz, so not too shabby! Interestingly enough, the last time we reviewed a Black Edition AMD processor, the Phenom II X4 965 BE back in August of 2009, we also received an 800 MHz overclock!
With this overclock, we were able to shave off another two seconds (Stock: 11.296 seconds; OC: 9.373 seconds) off the 32M wPrime benchmark to give us a 17% performance boost in that benchmark. This brought the Phenom II X4 975 BE very close to the performance level of the Intel Core i7 875K.