TechPowerUp posted a review on the Intel Core i7-7740K Kaby Lake-X Cracks 7.50 GHz on Liquid Helium
A quote from the article:
TeamAU with GIGABYTE OC Lab successfully overclocked an Intel Core i7-7740K "Kaby Lake-X" quad-core processor to 7.50 GHz. Only 2 out of its 4 cores were enabled for the feat. A Gigabyte X299 SOC Champion was used for this feat, and liquid helium was used to keep the CPU cool. The overclockers dialed kept the base-clock constant at 100 MHz, while dialing up its multiplier to 75.0x, yielding 7.50 GHz. Its core-voltage was kept at 1.096V.Intel Core i7-7740K Kaby Lake-X Cracks 7.50 GHz on Liquid Helium @ techPowerUp