getting your latencies lower maybe possible but it really won't help much. If you think it has it in it, I would try raising the CPU Ratio Setting to 21. You'll have to raise your voltages back up but that will put you at 4.2 GHz with your memory still at 1600MHz.
Why don't you increase your ratio to 21 anyway, just for funsies Like Slay said, you'll need to knock your cpu voltage up probably two notches, but apart from that you don't have to change anything else. See what kind of temps you get