It was shocking...
Then I realized those numbers were total system power, not just GPU power.
So, under Furmark, the normal GTX 480 pulls 304 watts more than it does at idle. An educated guess as mentioned puts the GTX 480 at around 60W idle? If that's true, then the NORMAL card was pulling 360 or so watts under load.
An extra 194W for the 512 CUDA core version means . . 554 watts under load. Ouch!
@drivinfast247 - so, if the legacy performance hierarchy is accurate, even if it did perform on the level of a GTX 580, we're still talking below RX 570 performance. More like 1050/1050Ti, or RX 560-4G, R9 280/285 level.