I don't know how to say nicely that you don't realize how ignorant about the field you must seem to anyone who isn't. You'll have trouble finding such comparison for the same reason you won't find a "caterpillar vs motorbike" speed test easily. Everyone in the target market including Apple knows hardware encoding will never be about output quality.

Anyway, here, I'm feeling nice. Some guy comparing the M1 Pro's HEVC encoder vs x265 (amongst others): https://colinmckellar.com/2024/01/11/video-encoder-compariso...

Here's the only graph you need to look at if you don't want to bother (encoding time vs file size at fixed perceptual quality, log scale axes): https://colinmckellar.com/wp-content/uploads/2024/01/VMAF_90...