You can change the memory divider, and manually set RAM voltage and timing per spec, but the experts have warned that the memory controller is not designed for more than 1333MHz. Translation...it can be tricky to run at 1600MHz (higher NB voltage), and you may fry the CPU over the long run.
I've opted for a 10% bump over 1333MHz, then lower the timing. My memory is running at 1460MHz with 1.65V and 7-7-6-20-27-1T.