I had one stick of 8GB of ram at 1600 MHz, and I recently bought another stick of 8 GB from the same company to upgrade my ram on my PC. However I realized that the new one that I bough was 1866 MHz. If I use them both together would it simply run the 1866 MHz ram at speeds of 1600 MHz? Or should I expect compatibility issues and simply buy another stick of 1866MHZ and not use the 1600MHZ