After much prevarication, I decided that I should stick with the PC. One issue was that, even if the machine is much faster, using external HDDs would slow things down, and testing all my external drives,I decided they would all be significantly slowr than the internal ones on my PC.
The first step in “upgrading” was to move the folder containing files I am working on to a fast SSD. Coming from Lightroom, I was used to the idea that it was fine to store photos on a regular HDD provided that the app and catalog were on a fast SSD, but I think with PL5 it makes more difference having the photos on a fast drive, presumably because of writing .dop and .xml files. That improved a lot of PhotoLibrary actions that I had found frustratingly slow, like keywording. I tried an external SSD rated at 1000MB/s, but was not getting that sort of speed despite using what I think is a fast USB port, so I ended up using the internal one I had reserved for catalogs.
Then I decided to follow Torstein’s advice and upgrade the graphics card and bought an ASUS DUAL-RTX3050-OI8G. This was the fastest I could install without needing to upgrade the computer’s PSU. It has certainly improved export speeds though, from what I read, not by as much as an M1 Mac would have done. But then it was not so expensive. Where I notice what I think is a bigger difference (I should have timed PL5 exports before I removed the old card) was in Topaz sharpening, which seems much faster. One of my reasons for frustration with the slow export speed was that I often export from PL5 using DeepPrime, then sharpen in Topaz Sharpen AI, and then come back to PL5.
So far I have assumed “Automatic” will use the GPU when it is faster, though at some point I may select the GPU to make sure.
One point is that the card is “semi-fanless” and turns off below a certain temperature. It appears to remain off all the time, but comes on, not too loudly, when Topaz is processing. I guess if it didn’t it would mean that I did not need the faster card!
So on the basis of an hour’s use, it seems a worthwhile upgrade that will keep me happy for a while. Thanks to those who gave me advice earlier this month. Of course, the new Mac may still come at some point, but probably a Macbook that is primarily for other things, rather than a Mini.