The alleged RX480 numbers also give a factor of 4 range in the voltage and clock product between the lowest power state and turbo, and 2.5-2.6 for the power state equivalent to Neo's rumored clock.
At an admittedly idealized level, the V^2xC product would give a rough picture of how much more power each state consumes than the previous, with the question of where in the range of leaked power states the GPU was operating in. The greater the portion that the leaked power numbers come from the least-efficient power states, the more Neo could improve by operating in the 911 MHz range.
Neo's rumored RAM speed is also modestly lower than the RX480's, which gives some additional wiggle room for the APU+DRAM power budget, which would be the largest contributor.
Since Neo is also supposedly the premium option, it might be able to adjust the investment in the cooler in order to allow for peak draw that is close but not equal to the PS4 at launch.
Of a 5.5tf Neo?