When people say x86 is not power efficient, it usually means it’s not very efficient for battery powered devices, or is kind of wasteful in situations like in data centers where they’re running thousands of machines. For home use, with a machine that’s gonna probably end up idling most of the time, my best guess is it would cost you a couple tens of dollars a year to run vs a slightly smaller amount.

Personally, just so I don’t have to deal with software compatibility on different architectures, I’ll gladly pay that small difference in power usage, but this will of course vary depending on what you’re looking to run on there.