I think this is a new record (125 H/s/watt): reddit.com/r/MoneroMining/comments/htpdqp/turnkey_mining_rigs/fyiysks

impressive

I suppose you could get slightly lower power draw out of a purpose-built mining motherboard.

leave a bunch of peripherals unpopulated.

make a serial console over USB, no GPU at all, no extra PCI slots

boot from eMMC

soldered DRAM

etc...

typical SBC