Thanks for all your feedback folks, I decided to go for the extra 32GB, it should be arriving tomorrow.
This is all rather fortuitous though, as since my OP, I’ve noticed that my system silently crashes/freezes and a motherboard diagnostic LED indicates a problem with the Ballistix RGB RAM, so I’ll be replacing it with the extra RAM to see if that resolves the issue, if so I’ll be returning the faulty RGB RAM for replacement.
If anyone is wondering about RAM on an Intel iMac 5K 2020, 64 GB was more than enough, even with DaVinci Resolve, PhotoLab 5, browsers and helper applications open. I only ever used up about 45 GB.
On an M1 Pro MacBook Pro, the 16GB version was not enough. With the 32GB version, PhotoLab 5 has taken up as much as 15GB alone, even with regularly quitting it. DaVinci Resolve behaves similarly but not because of a memory leak in Rosetta like PhotoLab 5. Generally I try not to run both at the same time. As long as I don’t run PhotoLab 5 at the same time as a full video editor, I don’t run into any memory issues with 32GB even with lots of browser tabs and helper applications open.
I understand this thread is specifically about AMD architecture and the Windows version but the thead title is general – “Do I need more than 32GB of RAM?” so I’ve added the Mac side for those who might stumble into this thread looking for advice and because I happen to have first hand data at my fingertips.