Mainboard accepts DDR4 2666, while the CPU is compatible with DDR4 2400.
Mainboard accepts DDR4 2666, while the CPU is compatible with DDR4 2400.
You already own certain components, others you plan to purchase. Most BIOS options let you adjust the RAM speed between 2133MHz and whatever you specify, yes—but if you're unsure or haven't bought parts yet, stick to what the CPU supports. The choice depends on whether you intend to upgrade later.