(the Copy to: and Organise by: are not separate processes, they are the import settings used to tell LR where to put the DNG files. So LR was doing these operations:
Read raw file (Disk Operation)
Convert to DNG (Processor Operation)
Write DNG to disk (Disk Operation - that should be carried out in parallel to the conversion)
Preview Generation - (Processor Operation)
Write Preview to disk (Disk Operation - again, should be done in parallel to Preview Generation)
As explained in the thread, I did this test as a request by another member. I'd assumed that creating previews would be a processor-intensive operation and would show a minimal difference. I was wrong, holding the images on an SSD it took 0.6 times as long to generate previews as when the images are held on an HDD.
Now this was some time ago (over 3 years) so I wouldn't be at all surprised if LR had been re-written so that these differences were no longer so huge.
