Overclocking our old Sandybridge-E was simply a matter of raising the multiplier while adding incremental voltage changes until the processor until the sliver of silicon ran out of steam. At this point we would raise VCCSA and VTT along with adjusting PLL voltages. For some reason the 3960X we sampled a couple of years ago did not respond kindly to either baseclock adjustments or changes in the CPU strap. Both would result in none booting scenarios. We did however on occasion manage to reach 5GHz although at 1.5v on the Vcore we wouldn't advise running this voltage 24/7. Instead we opted for 4.5GHz as our 24/7 voltage which seemed happy with a much healthier (but still very high) 1.42v.

Two years on and with the 4960X being cooled gently by our test setup H100 which we feel is representative of high end air cooling performance/low end water we set about overclocking this CPU.



Intel have made some small changes to the processor overclocking architecture as stated above so we were intrigued to see if this CPU could be pushed further than its predecessor.





Above you can see the starting point with the reference and Turbo Boost clockspeeds.

We started out by adjusting the CPU strap to 1.25 which unlike our 3960X caused the 4960X no such problems. We then played around with the baseclock which again, the 4960X responded well to although anything above 105 proved unstable.



Reverting to the tried and tested method of simply adjusting the multiplier and vcore, we hit a wall at 4.3GHz. Undeterred, we played around with a combination of PLL, VCCSA, VTT voltages along with loadline calibration and managed an impressive 4.923 GHz! We have no doubts that under extreme cooling 5GHz would easily be surpassed. Unfortunately at this screaming speed, a very high (unsafe) voltage of above 1.5v was needed to stabilise (8hrs Prime95) and while temps were within spec (71c), we would not be comfortable running this voltage 24/7 on low end watercooling/high end air cooling as the silicon would likely suffer from electron migration and thus degrade over a shorter period of time.



So, we dialled in a Vcore we were more comfortable with (1.4v) and after a day tweaking settings, testing, re-testing and benchmarking, we settled for a very respectable 4.8GHz.