You can manually adjust ram speed by increasing the spd system memory multiplier to give you 1600mhz,also set dram voltage to what's printed on the ram,either 1.5v or 1.66v,make a note of what auto sets qpi/vtt voltage to,as the more ram and faster the speed the more qpi/vtt voltage you will need to cope,for 12gb I would test with between 1.35-1.42v qpi/vtt voltage