maybe your MB downclocked the RAM?
Even if it is downclocked, you should be able to crank up the speed to 1600 and run it without errors if it is true ddr3 1600 ram.
I guess right now you speed up the RAM by increasing the memory multiplier? Can you try to get it to 1600 just by increasing the baseclock. To keep your cpu at the same level you can lower the CPU multiplier. Give that a try