Your RAM is running at 1333 ( DDR = Double data rate 667 * 2 = 1333 )because that's what the onboard memory controller on the i5 2500K defaults to. If you want it to run faster you will have to set it manually in BIOS.
You should make sure that your memory is 1.5v because going over that voids the CPU warranty. Technically going over 1333 speeds also voids the CPU warranty. Going over 1.5v or 1333 speed overclocks the onboard memory controller on the CPU.
I have not seen anyone have problems running DDR3 1600 as long as it was 1.5v but especially with older P67 boards some people have problems with runnings speeds faster than that. Going over 1.5v can damage the CPU.