> Up until this (theoretical) machine,
A little earlier than that. With Intel's Lunar Lake / Panther Lake, x86 laptops are again in the same ballpark as a Mac efficiency-wise. There are reputable reviews where people are getting 16-20 hours of battery life out of them doing real work, in both Windows & Linux.
M5 is probably still better, but at least the x86 machines don't embarrass themselves any more.