I’m looking at used machines for a cheap Plex server. The UHD 620 machine costs a fair amount more than the 520. Is there any significant difference in quality when transcoding to AVC?
QuickSync performance is not an issue, it won’t ever transcode more than 1 video at a time, so CPU performance in audio transcoding is also not an issue. I also don’t care that the 520 won’t decode HEVC 10-bit. Quality is my only concern here.
IIRC the key difference will be that Intel only started to fully support 4K HEVC with QuickSync with its Kaby Lake generation of microchips. The Graphics HD 520 predates that.
That should be about it with regards to your everyday transcoding.