Back when Fry's Electronics was still around, they had a sale on old AMD MSi AM1 motherboards and Athlon 5350 quad core 2 GHz CPUs (APUs) for $45 or so for a set. I bought quite a few, and now I regret not buying more. At 100% CPU load they take less than 25 watts measured at the wall, and less than 40 watts with two spinning rust 3.5" disks. They make excellent NAT routers / firewalls / DNS servers, et cetera. They can route / NAT a full gigabit and still have cycles to spare.

The closest thing we have today is getting a quad core Ryzen and running sysctl -w machdep.cpu.frequency.target=1600. Personally, I'd rather have more of those wonderful 2014 motherboards and CPUs.