At any given moment I have two drives hanging off my iMac. Fanless. 
I’m so sensitive to fan noise that I chose the Retina iMac with i5 processor instead of i7 because of reports that the i7 was spinning up the fan when people scrolled, and Intel poo-poohed complaints on its Windows-centric forum boards while acknowledging it and claiming it was “normal”, resulting in a furore.
In 2.5 years I’m not sure I’ve really ever heard the fan on my i5 iMac, so it ended up being the right choice for me.
At the time neither Lightroom nor Ableton supported hyperthreading, so I didn’t need the i7 processor. These days both apps do, and I’ll undoubtedly get some upcoming iMac with an i9 processor, as the current i9 iMacs appear to be pretty quiet.