Noflashing bios just stock bios.
All 8gb cards below
R9 390. Can do 32mh at 250 watts
Rx 480 can do 27mh at 150 watts
Rx 470 can do 25 mh at 140 watts
Those are pushing with. overclock and under volt.
Gigabyte Windforce GTX 1070 8MB - 55 Mh for *2* cards at 146/151 watts (151 is the card that is running the monitor), small memory-only overclock stock bios and no serious effort made at tuning yet.
Win 7, 372.70 drivers
Temps around 60c at about 80% fanspeed in a room that's usually around 82f.
(no, it's not PRICE competative with the RX 480/470, but I've got longer range plans for that machine that dictated a NVidia solution but cost less than a single Titan X Pascal for same-to-slightly better performance).
I wasn't comparing CHEAPEST 480 to CHEAPEST 470 - but I have seen some of the cheapest 480s on NewEgg dip a hair below some of the more expensive 470s - thus my comment about the price RANGE overlapping.
And yes, this CAN happen on the same brand when you include comparing both 8GB and 4GB models, though it's not common.