As long as the buss speed is the same you will be fine. (MHz)
Just make sure both have the same voltages and speed and you will have no problems.
Most MOBs will match the timing of the RAM, so you will not need to set anything.
It will default to the slower RAM throttling the faster RAM down.
becuase both RAM stick are 1600 MHz you will be fine.
Check your MOB's RAM compatibly chart to make sure that RAM is supported.