The current Apple iMac offers a great 5K screen, a good looking aluminum case, and great speakers. However, the all-in-one struggles to utilize the full potential of the components. You should be careful with the boxes you tick when you buy an iMac.
https://www.notebookcheck.net/The-optional-Upgrades-for-the-Apple-iMac-27-are-not-worth-it.503534.0.html
When are Apple's upgrades ever worth it? The hardware is locked down and many components are soldered and glued. If you do not upgrade at the time of purchase, you are captive to whatever you are stuck with.
The topic is interesting, however, its just an opinion, there are no hard facts/figures. So its just clickbait.