Five of the six motherboards we tested pushed our Core i7-4770K sample to 46 x 100 MHz stably under an eight-thread, AVX-optimized Prime95 load. MSI’s Z87I was down by half a tick at 45 x 101 MHz.
We generally limit ourselves to multiplier-based overclocks whenever possible, so the only base clock that matters to most of us is at the processor’s 100 MHz strap. That’s because locked cores also have locked straps. A non K-series processor can still get a 9% overclock from Asus’ Z87I-Deluxe, in addition to the four 100 MHz bins of headroom available to those processors.
ASRock falls slightly behind the top three boards in DRAM overclocking, but Gigbyte’s Z87N-WiFi had a more-serious issue of instability at high memory multipliers. But we’re not sure this matters, since our recent DRAM tests showed that timing-optimized DDR3-2133 offers slightly better performance than timing-optimized DDR3-2400 with Haswell-based CPUs.