HEVC does wonders for file size at a respectable quality. I used to aim for 10GB for a 1080p H264 film, now fine with 2-3GB. Doubt I can really tell the difference. Neither my eyes or TV are good enough.

Exactly. 

Doing a TV series from Blu Ray recently. I did season 1 in H.264 as usual and was pleased to see 45 minute episodes coming out at around 5 GB. Then I did season 2 with H.265 (at a higher bit rate) and they went down to around 2 GB, and appeared to be identical or better. So I redid season 1.

Had a moment of doubt just now when I saw what Amazon's "the Vast of Night" looked like: all washed out with grain and blocky distortion in the greys and blacks. Not that the black was especially black. Then I had a squint at the 4K stream on my telly and it's pretty nearly as bad. Whether that's as intended, for the authentic vintage atmosphere, or Amazon's dreadful HDR implementation, or both, I have no idea.

I've been sticking with H264 for now - primarily because my Raspberry PI doesn't support hardware decoding of H265, so framerate is poor for those. At some point I'll upgrade the PI as the latest ones do support H265 decoding in hardware.

I didn't know the latest Pi did H265. That's quite impressive. Bet it runs hot. My laptop has an 8th gen i5 and seems to support H265 recording. I tried a section from "Life on earth" which was very impressive until it got busy with a flock of birds taking off. Then it was terrible: all blurred with blocky artefacts. I imagine it would do better transcoding a video where it isn't working on the fly.