I'm not saying this to turn this into a big HP debate, but I do want to point out that 612 instead of 762 is a ~20% loss, and ICE cars I've seen have had a 20+% loss from crank to wheel. I don't know much about EVs yet so I don't know if there would be an equivalent loss. I've never expected a car to actually put out the numbers they say because of the loss.
IMHO loss at highest power levels could be very high, while loss at low power output could be closer to 0. We don't know where the power is being measured. After line/inverter loss and/or even motor loss?
Again, the Model S is only one of 2 cars in the world (that I know of) that have ever had a power gauge, the other being the Bugatti Veyron.