I've been testing more precise settings for my R7-1700 lately after finally getting the RAM stable at its rated speed. Focused on finding a decent clock while keeping the power demand/noise low, I ended up settling for 3.8 GHz. Going up to the ca 1.4 V required for stability at 3.9 GHz didn't feel worth it, for a mere 2.6 % boost.
Load testing with Prime 95(In Place FFT for max power draw) I ended up at either a plain 1.30 V core, or a combined setting of 1.25 V togehter with a core LLC at 3. Both settings give a peak recorded core voltage of 1.384 V over the course of a 30 min test. (It was more common to see the voltage linger around 1.30 V.)
Out of curiosity I got 3.7 GHz stable with a plain 1.225 V core. A level of performance/power perhaps fitting a smaller system that doesn't have a cooler like this Noctua NH-D15S that I'm using.
I started out my testing using voltage offset values instead of set values, but that proved to be more temperamental stability-wise and I don't feel like taking it up again. Aside from wishing for a motherboard with P-state support I'm pretty much finished testing this setup.