Transcoding 100+ files from H.264 to H.265
The whole one day I dedicated to testing various scenarios. The following applies to this particular series in this particular quality, so I don't say it applies generally. So in this case the following applies:


file sizes at the very same settings with only medium and veryslow preset changed vary negligibly: ~ -10 MiB on average in favor of veryslow preset
visual quality at a very close look is rather the same in either medium or veryslow preset


One thing solved. I have changed the preset to medium.




at a very close look, the source videos are not in such a high quality as I thought, that explains why x265 compresses to almost 1/4 of the original size


Another mystery solved.

Provided I now transcode at 25 fps, I have raised the RF to 20.




RAMDisk does not provide benefit in this case, both for medium and veryslow preset; I ended up with RAID6 as the source and SSD as the output drive


The inconvenience of moving files to RAMDisk solved.



To answer the question, the CPU time was not spent well at all.