The retail versions of Intel's Haswell chip reportedly run hotter and sip more power than pre-production silicon. In addition, the processors cannot (allegedly) be overclocked to the same speeds, while retail chips are "around 15°C" hotter than pre-production samples.
According to PC Pro, at least four companies have claimed that systems built using retail versions of Haswell chips are incapable of matching the speeds observed on pre-production models, which are traditionally distributed to manufacturers for testing before an official launch.
For example, one company reported that it had easily overclocked pre-production chips from 3.5GHz to 4.7GHz or 4.8GH, but at least "40 or 50" retail chips had been impossible to overclock beyond the 4.2GHz barrier because of the high voltages and unsafe temperatures involved.
"PCs based on pre-production [speeds] of 4.5GHz have had to be dropped to 4.3GHz," said a rep of the above-mentioned companies. "There is a big difference in the overclocking potential between early Haswell samples and retail [chips]."
Unsurprisingly, Intel had this to say about the issue:
"The overclocking experience will vary from CPU to CPU, and from generation to generation, due to many different factors... We cannot guarantee a specific frequency. We continue to add new and exciting overclocking capabilities and we expect enthusiasts to be pleased with the unlocked 4th Gen Core processors."