I don't have doubts a "7 nm" port of RKL-S would get >50% perf/watt increase either, just look at Rocket vs Tiger on 10SF for some numbers, now count higher IPC plus small cores and it's definitely not out of reality to get 2x perf/watt even running at max stock performance.
Indeed lower PL2 is all that counts for long term power usage and this is going down, a good sign for once. Those 10 ms higher peaks might as well be neutered by good capacitors on MB and PSU, that I would advice for anyway.
As for comparison I think most will be done with the previous -S chips to put them in a better perspective, mobile sort of comes later and will have less noticeable gains, but gains nonetheless.