Open after burner and hit CTRL+F. This will bring up the Voltage/Frequency graph.
Using the RivaTuner overlay in games, find what your highest common frequency is and the voltage it runs at.
Now find that voltage/frequency point on the graph, and using the point to the left, bring it up to the same frequency as what you were getting in game. Test that it’s stable, while running at the same frequency, but the lower voltage.