Intel places a couple of restrictions on Haswell overclocking. You'll need to pay extra for a K-series processor, for example. Overclocking is also limited to motherboards based on the Z87 chipset—or is it? ASRock claims to have enabled overclocking on its H87 and B85 motherboards. This "Non-Z OC" feature can purportedly ramp clock speeds up to 4.8GHz with Core i5-4670K and i7-4770K CPUs. Normally, those chips top out at 3.8 and 3.9GHz, respectively.
Based on the above video of Non-Z OC in action, the feature appears to use multiplier tweaking to reach higher speeds. Clock speed options are presented in 200MHz increments starting at 4GHz, just like with the auto-tuned profiles on ASRock's Z87 motherboards. It's unclear whether manual overclocking is supported, though. The firmware shows separate CPU multiplier controls, which is at least encouraging.
The first ASRock motherboard with this feature is the Fatal1ty H87 Performance, but Non-Z OC will be implemented on all of the firm's H87 and B85 models. That's the plan, anyway. ASRock concedes that, because Non-Z OC is dependent on Intel CPUs, chipsets, and firmware, its future availability can't be guaranteed. Intel could probably close whatever loophole ASRock has found.
Motherboard makers have discovered ways around Intel's limitations in the past, and I'm happy to see the practice continuing. It would be even better if someone could find a way to enable overclocking on non-K CPUs, even if it were tied to Z87 boards. Only the non-K chips have support for TSX extensions and VT-d device virtualization, features that are frustratingly unavailable among Intel's overclocking-friendly processors.