Researching the very most efficient parts from Intel and AMD today, 3x the perf/watt would be more accurate. Operating at a 5-6W TDP, the 2018 Apple A12X gets a multicore Geekbench score of 4730. Operating at a TDP of 15W, the i7-1065G7 (Ice Lake) gets multi-core Geekbench score of 4865. This is on Intel's 10 nm process that's comparable to TSMC 7 nm. Near equal performance for 3x the power.
I'd expect a 2020 A14X or whatever it's called to comfortably beat what they could achieve in 2018, so getting 4-5x the perf/watt of Intel and AMD's best is what I'd expect when operating at similar points in the frequency/power curve. The A12X was around 4-5x the perf/watt of what Intel and AMD had out in late 2018.
Unfortunately I could only find this old chart [0] showing how power draw scales with frequency on Intel. However for the sake of demonstration it should be more than enough.
The chip needs around 25W at 2.5GHz and 200W at 4.7GHz. 8x more power for
1.88 times the performance. In other words Intel chips running at 2.5GHz are 4.25 times more efficient than Intel chips running at 4.7Ghz. No magic. Once Apple has chips that go this far they will suffer from the same problems.
Here is a slightly newer chart [1] that demonstrates a 57% increase in power consumption for a 500Mhz frequency gain (12% performance gain).
I'd expect a 2020 A14X or whatever it's called to comfortably beat what they could achieve in 2018, so getting 4-5x the perf/watt of Intel and AMD's best is what I'd expect when operating at similar points in the frequency/power curve. The A12X was around 4-5x the perf/watt of what Intel and AMD had out in late 2018.
https://browser.geekbench.com/v5/cpu/2639065 https://browser.geekbench.com/v5/cpu/2638528