Windows 8 may have an overclocking problem. The folks at the HWBOT competitive overclocking site have stopped accepting Win8 results due to questions about the validity of benchmarks scores obtained using the OS. According to the site, the problem is the real-time clock that defines the operating system's sense of time. "Microsoft made changes to how it measures time to be compatible with embedded or low cost PCs that do not have a fixed RTC clock," the site says, adding that those changes have made the OS "practically useless for (competitive) overclocking."
The problem appears to be tied to changes to the system's base clock frequency. The HWBOT team tested a Haswell CPU running at ~4.16GHz using two different configurations: 34 x 122MHz and 32 x 130MHz. Despite having a faster base clock speed, the 130MHz config was 1.5-7% slower than the 120MHz one. Changing the base clock also threw the Windows clock out of whack; lowering the frequency by 6% caused the OS clock to "lose" 18 seconds over a five-minute period.
Performance benchmarking requires accurate timing, so it's no wonder the HWBOT team has decided to deny results obtained under Windows 8. All benchmarks are affected, according to the site, though some platforms may be immune to the issue. One of the article's comments claims systems based on AMD's Trinity APUs keep proper time regardless of tweaks to their base clock speed.
The article doesn't mention multiplier tuning, suggesting that the problem is restricted to BCLK manipulation. If that's the case, most PC enthusiasts have nothing to worry about. Unlocked processors have made multiplier-based overclocking so easy that there's little need to push base frequencies above their stock speeds.