I'm planning to purchase RAM.
I'm planning to purchase RAM.
However, there are settings such as 1600 MHz or 1066 available... (This is noted in the CPU-Z documentation)
It's the "DDR" double data rate configuration – in CPU-Z it displays the actual data rate. For a DDR4 3200, it lists 1600Mhz. The reported 666Mhz is likely an older or different setting.
Discussing RAM speed settings with XMP documentation for beginners