System builders have reportedly been blind-sided by Intel's latest fourth-generation Core series processors, with retail models proving significantly different to pre-production versions previously supplied.Intel's latest Haswell chips represent a tock - the changing of the microarchitecture, rather than process node - in Intel's annual tick-tock development cycle . Based around an improved architecture, the processors include boosted graphics performance and improved speeds along with new instructions designed to further increase software performance. While the company is keeping its best innovation, its high-performance GT3e 'Iris Pro' graphics technology, for OEM-only parts supplied in ball-grid array (BGA) packages, it's clearly still hoping to make an impact with its more traditional land-grid array (LGA) parts.Sadly, the impact it's made so far has been somewhat negative - at least where system builders are concerned. Anonymous individuals from four UK-based computer manufacturers have spoken to our sister publication PC Pro with the news that retail Haswell parts are considerably less capable than the pre-production versions on which they had been basing their engineering work.Prior to each processor release, Intel produces a number of engineering sample chips. These chips are, theoretically, identical to the finished retail product, minus a few last-minute fixes that may be inserted to work around some bug or other. They are provided to hardware partners in order for pre-release engineering work - designing desktops, laptops, tablets and mobiles around the requirements of the part - to be carried out before mass production begins. This allows manufacturers to launch their products day-and-date with Intel's chip release.Sadly, it doesn't appear to have worked out quite that way for Haswell. According to PC Pro, manufacturers who produce pre-overclocked gaming systems have found that the retail chips they've just received are only hitting speeds of 4.2GHz to 4.4GHz stably compared to up to 4.8GHz with pre-production engineering samples.One manufacturer claims that pre-release chips marked as 3.5GHz parts were tested completely stably at 4.8GHz, but of the 40-50 retail units the company has tested not a single one has managed to reach above 4.2GHz without hitting unsafe temperatures or requiring too-high levels of voltage. Another firm has stated that it has had to drop plans to offer pre-overclocked Haswell systems running at 4.5GHz - a figure, again, planned based on engineering work carried out on pre-production samples provided by Intel - to 4.3GHz in order to ensure stability. '' the unnamed manufacturer claimed.Another manufacturer claims that retail Haswell parts are proving too hot to handle, stating that even while running at stock speeds the chips reach higher temperatures than the pre-production engineering samples - by around 15 degrees Celsius, according to the unnamed company's tests - or even the retail models of Intel's last-generation Ivy Bridge chips.Intel, for its part, has refused to comment on the specifics of the manufacturers' claims, stating only that overclocking is not covered by the its warranties and that companies - or individuals - doing so are boosting performance at their own risk. The company has also stated that the overclocking potential of a given chip will vary from batch to batch, but has provided no explanation for the apparent vast difference in heat output between pre-production and retail Haswell models.Our review of Intel's Core i7-4770K can be found here , and while we were able to get our chip up to 4.7GHz it wasn't without difficulty: despite using a Corsair H100i sealed-loop cooler, the temperature of the chip hit a whopping 98 degrees Celsius - giving us cause to question just how far a Haswell chip can be pushed for long-term use.