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.

https://browser.geekbench.com/v5/cpu/2639065 https://browser.geekbench.com/v5/cpu/2638528