I know this has been discussed on the Forum. I gather there is a sort of consensus that pushing the number of “parallel” processing threads (in the final Preferences tab) past about ½ the number of CPU ‘cores’ makes not much difference. This is my experience, too.
What I did not fully appreciate is how the choice of “Prime” or “Deep Prime” noise reduction affects the export processing time. On my 2019 iMac (27", i9 with 48GB of RAM and the standard Vega 48 GPU) when I select Prime – that I expected to be less of a burden on the processor – the export of either TIFFs or JPEGs is woeful (4 mins to export 10 images).
But I have found that choosing the more intensive “Deep Prime” processing — that is unnecessary on 90+ of my full-frame raw images since I’m careful about exposure — is a LOT quicker. Export takes about HALF the time (2.25 mins for the same 10 images). I speculate this is because Deep Prime pushes the work off to the GPU and leaves the CPU to do the rest of the image processing.
I’m guess you all knew this and maybe someone mentioned it previously. But I must have missed the ‘memo’.