The Tech Report found out that Intel will almost entirely limit overclocking support on its Haswell processors, forcing enthusiasts who want to overclock to get the more expensive K-series parts because the non-K series parts will no longer have limited multiplier control. One benefit of the new K-series is that they will have additional base clock straps, but the downside is that the K-series lacks the TSX extensions, as well as the VT-d device virtualization and vPro management features.
Intel says it's targeting non-K chips at "the business and consumer market where overclocking is generally not performed."
Based on what we've seen in our labs and heard from industry sources, K-series Haswell CPUs have less clock headroom than their Ivy and Sandy Bridge predecessors. The Core i7-4770K being tortured on my test rack peaks at 4.5-4.7GHz, depending on the motherboard, and it requires potent cooling at those speeds. A more modest 400MHz bump shouldn't require an exotic cooler, but getting it will require paying the premium for a K-series processor.
Buying a K-series Haswell processor will set you back an extra $20-$30 over the equivalent standard model. The Core i7-4770K is priced $30 higher than the Core i7-4770, while the Core i5-4670K is $20 more than the Core i5-4670.