Per the OP’s initial announcement, I wanted to follow up from my previous posts to say my 2019 iMac arrived Thursday, a week earlier than the original delivery date! I’m still setting up and reinstalling everything, as past experiences with migration and cloning introduced legacy issues resulting in eventual clean installs anyway.
As for the questions/concerns about thermal throttling, I have been reading a number of positive reports (so far) as these new machines are just being delivered. Many of these are preliminary benchmarks, though showing definitively higher single and significant multi core performance compared to a 2017 iMac, and even compared to baseline iMac Pros. And for reasons still being deciphered, no throttling issues are being reported (yet), which will be good news for some potential buyers. Here is one brief synthesis among several I looked at at:
My personal benchmark is that of going from dual core i5 processors on my 2014 iMac, to this beast, lol, though my orchestrations have rarely exceeded 40 tracks (averaging about 35 per my workflow). I suspect other inquiries in this thread reflect much larger templates of preloaded ilk, relative to potentially pushing this machine to its limit. To me, these benchmarks are more theoretical, whereas I know precisely what limitations my 2014 system has had, and hence how this upgrade was timely for me.
On a personal note, as I’ve spoken about my progressive blindness, the display is also much brighter and at a higher resolution compared to my 2014 first-gen 5KRetina display. This consideration is a huge factor for me, relative those debates about the iMac being all-in-one.