It might just be the combination of better branch prediction, TSMC 5nm, 8-channel memory, 16k pages, along with 8-wide cores+larger structures especially cache

It might just be the combination of better branch prediction, TSMC 5nm, 8-channel memory, 16k pages, along with 8-wide cores+larger structures especially cache are enough to account for the more perf/watt of the M1.