You can try it. I've mixed sticks in the past with good results, of differing speeds and settings, the computer will set itself to the lowest common speed for both kits, here's the rub, there's no guarantee they will work together even if all the settings on both sets are the same, it's just the way it is now with RAM. That's why so many sets are a pair or quad of sticks for dual or quad channel memory (three sticks for tri channel). When you buy a kit, it comes guaranteed that both sticks will work together. Anything else, *ANYTHING* else, and there's just no guarantee that they will play nice, no matter the motherboard no matter adjusting the settings, some sticks will just not play nice with each other. There is nothing to say...