ASRock isn't the only manufacturer allowing builders to overclock locked Skylake CPUs on its Z170 boards. Today, Biostar announced a BIOS update that enables this type of overclocking on four of its motherboards. For example, the company boasts that it's pushed a $65 Pentium G4400 up to 4.48Ghz—with the usual caveat that your results may vary. Owners of Biostar's Gaming Z170X, Gaming Z170T, Gaming Z170W, and Hi-Fi Z170Z5 motherboards should keep an eye out for this update soon.
This overclocking strategy is possible because of changes to the base clock domain in Skylake processors. Since Skylake's base clock is no longer tied to other on-chip clocks, overclocking the BCLK won’t necessarily cause problems elsewhere in the system.
Given Biostar’s announcement, overclocking non-K Skylake CPUs might be turning into an industry trend. Barring a response from Intel, other motherboard makers might be making similar announcements at some point.