According to the imac pro tech specs from the link you provided, it has an idle draw of 64W, and a peak draw of 370W for the entire system.
Unless I'm mistaken, that seems to imply that there has to be a good deal of throttling between the CPU & GPU to come in at that power budget. (The specs also note an additional 50W(!) of potential draw for fans alone if the imac is operated in a warm environment.)
Am I mistaken?
Not arguing, just hashing out my understanding. Your point regarding the Surface Book 2 and the 1060 makes sense. It does look like I was technically incorrect about them not engineering to a 200+ watt GPU, although I do wonder what sustained draw it can handle thermally compared to a full desktop part, and how much that would affect performance.
John from Mantiz reported 650W peak. Surely only for milliseconds but still. https://egpu.io/forums/implementation-guides/2014-mac-mini-v... it is absolutely not in the interests of an eGPU chassis manufacturer to report figures which hinder their own sales so I believe him.
Similarly, someone with an awful lot of AMD knowledge (AMD employee?) on the egpu.io forums pretty much begged people not to try the Vega 64 in a Sonnet 550 hinting at similar problems https://egpu.io/forums/thunderbolt-enclosures/sonnet-says-th... and saying a solution is in the works.
Sonnet http://www.sonnettech.com/support/kb/kb.php?cat=524&expand=_... says the Vega 64 is only supported in the 650 box -- which was just released pretty much because of the necessity to support the Vega 64. Something is rotten in Denmark: 650W power supply supports up to 375W card (up to 8-pin + 8-pin power connectors) plus provides additional 100W of peak power.
The AMD Vega 64 has got to push a few hundred watts.
Microsoft has the Surface Book 2 with GTX 1060 and they must be looking at that as competition for the high end MacBook Pro.