Confirmed today, I took apart my 2019 iMac base 6 core 8500.
Upgraded to Samsung 970 EVO Plus 1TB - No Issue with the Latest firmware 2B2QEXM7 released on 2019/5/20.
Upgraded to 12TB Seagate EXOS HDD - Have hdd fan speed issue, did not put the OWC sensor. Use Mac Fan Control as alternative solution.
Upgraded Ram Kingston KHX2666C15S4/16G - No Issue.
The CPU is changeable, not soldered - Not upgraded yet, I'm okay with 8500's performance so far. But I'm sure the CPU is upgradeable.
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=== Update (06/24/2019) ===
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Upgrade is fine, but the photos in https://www.instagram.com/p/BzF7bNoIreS/ seems has thermal sensor for the HDD.
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BTW, Zach, what is your normal idle fan speed after upgraded to 8TB HDD? Mine idle speed is about 1600-1700rpm, the fan sound is very noticeable. The lowest fan speed is 1200rpm, and the highest fan speed is 2593rpm from the Mac Fan Control settings.
Confirmed today, I took apart my 2019 iMac base 6 core 8500.
Upgraded to Samsung 970 EVO Plus 1TB - No Issue with the Latest firmware 2B2QEXM7 released on 2019/5/20.
Upgraded to 12TB Seagate EXOS HDD - Have hdd fan speed issue, did not put the OWC sensor. Use Mac Fan Control as alternative solution.
Upgraded Ram Kingston KHX2666C15S4/16G - No Issue.
The CPU is changeable, not soldered - Not upgraded yet, I'm okay with 8500's performance so far. But I'm sure the CPU is upgradeable.