So far every review I have seen (at it is in the dozens) state that the fan never becomes audible on the 8-core and 10-core no matter how hard you hit them unless you physically put your ear next to the vent or are in a truly-silent room. It sounds like the fans never need to spin up to an audible level they just move hotter air as components heat up.
If you have links to tests, that really test longer rendering, it would be interesting.
Eg. Barefeats have made lots of tests, that all are measured in seconds, not even minutes.
AI concludes: "With that said, it is a bit disappointing to see Apple prioritize noise over performance and thermals on a high-end pro machine."
It can also be, that cpu/gpu thermal envelope is now really limited and it will get more powerful with os updates to come.
Or Apple just might have chosen longer, colder lifespan for chips not easily to replace.
In AI's tests, the chips were nowhere near 100%.
Interesting also:
http://appleinsider.com/articles/17...d-with-the-imac-pro-with-more-in-the-pipeline
:"Preliminary
AppleInsider testing with a Vega 64 PCI-E card in our faithful
Mantiz eGPU enclosure is delivering about 10 percent more performance than the down-clocked Vega 64 chipset standard to the 10-core iMac Pro, and is far faster than the Vega 56 in the $4999 configuration."
It might very well be that iMP is a "corporate pro" in that way that rendering is supposed to be done in machine room, not inside iMP.
Apple did gave us heads up that "mMP is coming" (time is of course relative), but it would be fair for "personal pro" that Apple would promise solid support for eGPUs. In addition of assurance of epgu being stable from update to another, using real pci cards would give ability to go around that ancient dp1.2 that TB is cursed with before TB4 comes.
(EDIT: Oops, there it is:
https://www.apple.com/macos/high-sierra/#footnote-3 :"Planned for spring 2018." Well, planned... what does that mean in Apple language...?)