You want high frequency (that gives better performance) with as low a voltage as possible (higher voltage = higher power draw and heat).
1.3V is a lot for 4.7Ghz. If the heat is fine then that's not really a problem, it's just pushing the CPU and cooling harder than probably you need to. Generally you spend some time either maximising your frequency (if you want to get the best performance you can), or getting the voltage down as low as possible (to maximise CPU life and temp/noise levels.
Once you get instability or tests fail, that a sign that the voltage is too low for your given frequency, and you need to make a decision either to raise the voltage or lower the frequency.
Thanks for the detailed reply!
I might go back to my original 1.275 - 1.280 in that case, as it seemed to be operating okay at that.