motherboard - Why is my memory running at 665Mhz when the BIOS is clearly set to be higher? - Super User
Why Task Manager shows 1333 Mhz and not 2666 Mhz despite adding 2*2GB 1333 Mhz (DDR3 KIT) and CPU-Z shows Dual Channel & DRAM Frequency at 665 Mhz? - Quora
Speccy says my ram is at 665mhz - CPUs, Motherboards, and Memory - Linus Tech Tips
memory - What kind of RAM is compatible with my system? - Super User