In my ASUS EZ Mode BIOS, it has options for Energy Saving Mode, Normal Mode, or Performance Mode. I am not sure if you have options like that. For me, if Normal Mode is selected then I will have the 1600mhz option, if performance mode is selected the option is bumped to 1648mhz. Also the processor seems to be bumped as well. I am running mine on 1648mhz and everything is great, you can see if you have some sort of Normal Mode then set it back to 1600mhz if you like. When I made changes to the Mode it is in, I had to Save and Reset before you adjust the speeds.