Thanks - and fully agree - I didn't question N2's density advantage - was just curious about the power efficiency.
haha, fair -- My personal (silicon outsider) bias is that TSMC's processes tend to be the most efficient.. but at least from public info - 18A is looking pretty strong at efficiency, at least in certain scenarios. and same experience re: transistor density - but it's been almost decade at this point that TSMC has led in density

. Apple A12 shipped in Sept 2018 on TSMC N7.
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18A does have the thermal conductivity handicap of BSPD, so efficiency would be key to keep the total thermal density down. I'm guessing 18A was biased a bit towards efficiency, while 18A-P will be more biased towards performance (as Intel has said the new process improves thermal conductivity by 50% - which allows for more power per transistor).
That said, I feel like efficiency and "max clocks" on process nodes are converging -- to raise max clocks you need to improve efficiency to push voltage curve "up and out". Improving that voltage curve (say going from 1.1V to 1.0V at 5.0 GHz) certainly helps efficiency under load conditions, though idle power may be a different story.