After weeks reading this forum, I have a brand new iMac 2019 27" i9 Vega 48 40gb RAM 500gb ssd. Here in my country (interior of Spain) temperatures outside this week have been up to 44° C or 46° C (at 8h00 am the temperature today was already 32° C), inside I have no AC in the recording studio and temperatures can easily reach 35° C. In winter we can reach -15° C outside 
I have been testing the new computer these days with the commented operating temperatures, using very CPU intensive processes for music production mainly (lots of demanding virtual synths and DSP effects). I am a music producer/advanced data analysis consultant and I have to admit that I am very sensitive to faint sounds and noises (so the computer noise is a real concern for me). This i9 imac performed extremely well and dead silent under lots of CPU stress tests so far using last generation demanding virtual synths and realtime DSPs. My study is very quiet, with specific acoustic treatment. The software that I use is normally optimised for multiform and multithread CPUs (the i9 is perfect for this). I could not hear the fan yet (except when I changed manually the fan speed using a fan control soft). CPU temperatures are practically always below 52° C during my normal music production sessions so far, even with these high room temperatures.
This machine is a beast for music and audio production. In some CPU tests I have reached counts of tracks of +500 virtual synth tracks with demanding effects (reaching approx. 60° C or 65° C) and with no fan noise.
I am very and positively surprised with this excellent computer. It works flawlessly with my audio interfaces. I heard that the macs with T2 chip had some potential issues with external usb audio interfaces, so for me the absence of the T2 chip is welcome.
I was, as many other forum participants, not decided between this machine and the base iMac Pro. And I think that I made the right decision with this i9 2019 iMac (my multicore CPU Geekbench 4 score is close to 34,000). A silent and powerful computer is what I needed for my studio.
As I commented, I had to use a software (Macs Fan Control) to manually increase the fan speed in order to be able to hear the fan, in order to check that it was there and operating and even at max speed (artificially set by me) the sound is not intrusive or annoying at all for me (it is a sort of background constant white noise, the type that some people use to get relaxed and asleep).
I also have a 2010 mbp i7 that sounds much louder and noticeable at full fan speed than this new iMac. So temperatures, CPU performance and fan noise would not be real concerns for me with this new iMac, based on my experience.
My next tests with the computer will be in the advanced analytics realm, trying to use the CPU and GPU for machine learning applications, deep learning with the Vega 48 and advanced data modeling. So far I am very satisfied with this iMac.
I have been testing the new computer these days with the commented operating temperatures, using very CPU intensive processes for music production mainly (lots of demanding virtual synths and DSP effects). I am a music producer/advanced data analysis consultant and I have to admit that I am very sensitive to faint sounds and noises (so the computer noise is a real concern for me). This i9 imac performed extremely well and dead silent under lots of CPU stress tests so far using last generation demanding virtual synths and realtime DSPs. My study is very quiet, with specific acoustic treatment. The software that I use is normally optimised for multiform and multithread CPUs (the i9 is perfect for this). I could not hear the fan yet (except when I changed manually the fan speed using a fan control soft). CPU temperatures are practically always below 52° C during my normal music production sessions so far, even with these high room temperatures.
This machine is a beast for music and audio production. In some CPU tests I have reached counts of tracks of +500 virtual synth tracks with demanding effects (reaching approx. 60° C or 65° C) and with no fan noise.
I am very and positively surprised with this excellent computer. It works flawlessly with my audio interfaces. I heard that the macs with T2 chip had some potential issues with external usb audio interfaces, so for me the absence of the T2 chip is welcome.
I was, as many other forum participants, not decided between this machine and the base iMac Pro. And I think that I made the right decision with this i9 2019 iMac (my multicore CPU Geekbench 4 score is close to 34,000). A silent and powerful computer is what I needed for my studio.
As I commented, I had to use a software (Macs Fan Control) to manually increase the fan speed in order to be able to hear the fan, in order to check that it was there and operating
and even at max speed (artificially set by me) the sound is not intrusive or annoying at all for me (it is a sort of background constant white noise, the type that some people use to get relaxed and asleep). I also have a 2010 mbp i7 that sounds much louder and noticeable at full fan speed than this new iMac. So temperatures, CPU performance and fan noise would not be real concerns for me with this new iMac, based on my experience.
My next tests with the computer will be in the advanced analytics realm, trying to use the CPU and GPU for machine learning applications, deep learning with the Vega 48 and advanced data modeling. So far I am very satisfied with this iMac.