NVIDIAGeek, Rams of different speed will run simultaneously on your system and at the speed of the lower one which is 1333 MHz in your case. But most of the 1333 MHz Rams from brands like Corsair, G-Skill, Kingston and even Transcend are capable of running at 1600 MHz speed. But you need to make sure they have same Cache Latency for stability. Rams with different Cache Latency causes serious stability issues and they are not easy to change as easily as the speed can be. What Motherboard you're using currently?