Thanks for the feedback LoyceV, less than 10W is absolutely impressive and far lower that I'd have expected.
Note that this is without heavy load, but most of the time the CPU is (almost) idling anyway.
Shouldn't ARM-based laptops (Chromebooks, Windows 10 ARM, ...) even be able to undercut this value?
I have no experience with those, and especially software compatibility. I like "the standard" that just works.
Wikipedia has a list of low-power CPUs. The Atom stands out (but is slow), the Celeron is slow but sold in massive numbers, the i3 and up come with different power and speed ratings.
My rule of thumb: if the device doesn't get warm without using it's fan, it can't use a lot of power.