1600 is the "data rate". This corresponds to a RAM clock of 800MHz. Yours is at 666 MHz which means it's running at 1333 (data rate).
If you've set your memory to run at 1600 (data rate) in BIOS, it looks like your memory controller is overriding your BIOS setting. It may be that your memory controller cannot run 16GB of RAM at 1600. I'm not very familiar with Intel memory controllers. If you can disable XML in BIOS, that may remove the override.
Also: The data rate and RAM clock are not "timings". "RAM timings" refers to another set of metrics which includes Cas latency. Vocabluary Nazi, ho!