A quick look at power consumption and efficiency
We can get a rough idea of how efficient these chips are by monitoring system power draw in Blender and using that information to fill in the blanks on the convenient fact that one joule equals one watt expended over one second. Our observations have shown that Blender consumes about the same amount of wattage at every stage of the bmw27 benchmark, so it's an ideal guinea pig for this kind of calculation. First, let's revisit the amount of time it takes for each of these chips to render our Blender "bmw27" test scene:
Next, let's look at the system power draw from the wall we observed during our testing:
By a small margin, the Ryzen 7 2700 has the lowest system power draw of this bunch while rendering out our bmw27 test scene—13 W lower than even the Ryzen 7 1700.
Instantaneous power draw doesn't tell us much about how efficient a CPU is, though. Some chips will take more time to finish this workload than others, and a slow chip that doesn't seem to draw a lot of power at a glance will ultimately consume a ton of juice if it's running a workload for days at a stretch. Conversely, a power-hungry chip might finish a task much faster than slower, less-power-hungry parts, ultimately expending less task energy overall.
Our estimates of task energy expended over the course of our Blender workload put the Ryzen 7 2700 on top. By our estimation, it expends slightly less energy than even the Core i7-8700K and i7-8086K while delivering even slightly better performance. That's an impressive result for the 65-W second-generation Ryzen eight-core part.
This scatter plot might help visualize our results in a different manner. The best results on this chart would, in theory, gather in the lower-left corner, where task energy is lowest and time-to-completion is fastest. What we're really showing here is Pareto efficiency, though: the various balances between task energy expended and time to completion that each of these chips strikes.
If you care the most about low task energy, the Core i7-8700K, i7-8086K, and Ryzen 7 2700 are the clear winners on this chart. To get better performance, as the Ryzen 7 2700X and our overclocked chips deliver, power consumption over the course of the task climbs significantly.