Intel's quad-core Core i7 870 is a great all rounder. Short of a six-core monster machine, it's a hard to imagine what can beat it. However, for overclocking enthusiasts it does lack one key feature: an unlocked CPU multiplier.
Enter, therefore, the new Intel Core i7 875K. It's identical to the 870 save for a slightly elevated price tag and an overclocking friendly unlocked multiplier. The multiplier, of course, is a ratio that combines with the chip's base clock to generate the overall operating frequency. Crucially, it's not linked to any other part of the system and theoretically allows a chip to be overclocked without knock-on effects to subsystems like buses and memory controllers.
Anywho, if clocking the twangers off CPUs is your bag, an unlocked multiplier is a bit of a no brainer. For everyone else, it arguably just makes the Core i7 875K that little bit less competitive with the likes of AMD's Phenom II X6 1090T Black Edition.