What voltage are you at when you bump your BIOS to run at 1600MHz? That memory is good from 1.5v to 1.6v. You are probably needing a bump up to run at that speed (closer to 1.6v).
I'll have to double check. When I select the 1600mhz profile in BIOS I receive a notification that the RAM might consequently require higher voltage. It then asks whether or not I will allow an increase in voltage. I always say yes, though I don't know off the top of my head what it comes in at after I boot @ 1600mhz.