I’m currently helping someone who has a late 2013 iMac and it’s currently running Mavericks. The plan is to update it! Is it worth updating it all the way to Catalina or would it be better to stick with High Sierra? Does anyone have any experience of running this age machine using late operating systems? Do they slow it down significantly?
I have a healthy dislike of High Sierra. From a pure OS perspective, I would tend to stick with Sierra or go all the way to Catalina. That doesn't take account of the age of the machine, of course.
APFS is also still a little unproven long-term on rotating disks so that might sway you to staying with Sierra/HFS+.
Mick Burrell 