If they're using a GPU that is based on the the RX 480 it is probably going to be clocked lower, so possibly somewhere around 900MHz as the leaks suggested or maybe even 900-1100MHz .
I think above 1000MHz is unlikely, however it depends on how far Sony want to push it.
Even with this GPU at 911MHz the PS4 Neo could potentially consume more power than the standard PlayStation 4, however it depends on what clock-speed and voltage the GPU is running at, along-side the power consumption of the other components.
The PlayStation 4 was designed to be pretty power efficient and small, the whole reason it has a two prong connector is because they wanted to keep it under 250W to make the PS4 small in size.
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Sony’s engineers were instructed to keep the PS4’s power consumption strictly under 250 watt, and Ootori-san stressed on the importance of that choice. You’d think it was taken to limit the generation of heat, or maybe to simply help us save on our energy bills, but that’s not the primary reason.
Ootori-san explained that 250 watt is the upper limit, by safety regulations, that allows the use of a two prong power cord. By using 250 watt or more the PS4 would have required a three prong power cord, and of course a three pin power inlet on the back of the console. That kind of connector is larger, and would have negatively impacted the miniaturization of the unit.
That’s why Sony put its best designers at work on making the console as power-efficient as possible in order to keep consumption under 250 watt.
The 7870 and 7850 don't even pull above 150 watts in power consumption, the 7850 pulls around 90-100w, while the 7870 pulls a little above that.
The RX 480 is looking to pull above 150 watts, however that's at a clock-speed of 1266MHz.
The 7870 is clocked at 1GHz and has 1280 stream processors whereas the 7850 is clocked at 860MHz and has 1024 stream processors, they are both based on the 1st Gen of Graphics Core Next.
The PS4's GPU is clocked at 800MHz and has 1152 stream processors and appears to be based on a newer version of GCN which is something akin to the 2nd Gen of Graphics Core Next.
If someone was to under-clock and under-volt the RX 480 we could possibly see how the power-consumption scales, this could potentially tell us what we could see in the PS4 Neo.