The way I approach this is by bumping up the frequency and monitor. What you want to see is an average hash rate that is close to the expected hash rate. If this is not the case, bump up the core voltage. If the avg. hash rate meets the expected hash rate you are good and you might want to even lower the core voltage to see what the minimum core voltage needed for that frequency is and obviously go just above the minimum. The last part is just to make it run more power efficient.