For those looking for the efficiency peak, there is a good technical write up on Ryzen's voltage scaling on Anandtech: https://forums.anandtech.com/threads/ryzen-strictly-technical.2500572/

The most efficient range is below 3.3GHz (critical 1) where voltage and clockspeed scale linearly. Then there is a bump between 3.3 - 3.5GHz (critical 2). Above 3.5GHz, the voltage scaling becomes steeper. Then beyond 3.9GHz it gets exponentially more inefficient to push the clockspeed higher.

If I were to prioritise energy efficiency, I'd probably want to run the Ryzen 7 at 3.3GHz and about 1.025V. At these levels you can go with the 1700 non-X model, and even the stock Wraith cooler that comes with it would be more than enough.