Different chips with identical feature sets and performance/watt ratios, that's what I'm trying to figure out. So far the only difference mentioned by anyone was your "optimized geometry engine", which somehow doesnt convince me Vega 12 (that's the correct name, right?) is 50% more efficient than Vega 10.
I have a big problem with that "optimized geometry engine"...
Big Vega is famous for its Geometry Engine, that is capable of discarding primitives, that are not visible in the field of view of 3dGraphics(in games), and increase the framerate this way, and mitigate the fact, that there are only 4 Shader/Geometry Engines in the design, which massively bottlenecks the front end of the GPU, considering that 4 Shader/Geometry Engines, have to feed 64 CU's(each SE has 16 CU's).
The problem is... it does not work, at all. NGG path is completely disabled for Vega, and will NOT be available in any way, shape or form for Vega. Yes, Vega 12 is better design than Polaris 11, because you get 4 Shader Engines, which means with each clock, you will get 4 primitives, instead of just two, so the GPU will not be bound on the front end. But, Im not sure it really has "Optimized Geometry Engine". Primitive Shaders, Primitive Culling is coming back with Navi. Without some very specific hardware features(Operand Reuse Cache, or whatever it will be called by AMD), it is impossible for AMD to do what they wanted to do through drivers.
Apple themselves on their site says: "Enhanced Compute Engine" which relates to simply Rapid Packed Math: FP16x2 from FP32 cores, compared to FP16x1 from FP32 cores.
I was personally expecting much worse from Vega 12 in terms of core clock/core count in 35W TDP envelope. 1.3 GHz, from 1280 GCN core chip is pretty much unheard of, till now.
P.S. What matters for GPU power consumption and core clocks is ALWAYS physical design. Vega Mobile is different than Vega 10, for obvious reasons. Voltage curve is different, and MOST LIKELY, the fact that we have 4 Shader Engines, with just 5 CU's in each SE is playing the biggest role in so low power consumption of Vega 12, with such high clock speed. Yes, HBM2@ 1.5 Gbps is consuming just 3W's of power. But all the rest is due to good physical design(good engineering) from AMD.