TechPowerUp posted a review on the G.SKILL Trident Z 4000 MHz DDR4
A quote from the article:
The G.SKILL Trident Z sticks have been around for a while now, available in a multitude of colors and speeds, as well as with RGB. These 4000 MHz sticks are for all you non-RGB lovers out there, but with such a high speed, you best make sure your motherboard and CPU are capable.G.SKILL Trident Z 4000 MHz DDR4 Review