Find max stable overclock at stock voltage and stick to it.
Overvolting will hurt your power efficiency as the power usage rises by core voltage squared.
Power costs don't matter that much, its only 6% of profit atm. Also as I have worked on the problem some more, it seems I can't even raise the core from 725 or change it at all. If I change the voltage in afterburner I can see my hash rate start to rise but a split second later it drops back down to stock settings.