These firmwares disable power management completely, so that the microcode cannot even read the BCLK frequency and detect overclocking. As a side effect, you cannot use integrated graphics, and AVX instructions become slow — even slightly slower than at stock frequency (need power management to ramp up the AVX parts of the chip to full speed). But if you're not encoding video all day, you can save some money by buying a 6400 instead of a 6600K.
These firmwares disable power management completely, so that the microcode cannot even read the BCLK frequency and detect overclocking. As a side effect, you cannot use integrated graphics, and AVX instructions become slow — even slightly slower than at stock frequency (need power management to ramp up the AVX parts of the chip to full speed). But if you're not encoding video all day, you can save some money by buying a 6400 instead of a 6600K.