

This, @Thorned_Rose@sh.itjust.works.
I’m an audio engineer and can confirm that if you want the best quality audio for the file size, you want Opus. Opus at 128kbps is considered transparent, so it’s roughly as good as 320kbps MP3s, but y’know, less than half the size.
Generally this is true, but it depends on the encoder used. Back during the huge boom of MP3 popularity in the late 90s and early 00s, it likely did make a difference, so if you’re looking at MP3s that were encoded back then I would go for 320kbps every time just to be safe, but modern encoders generally do much better like you said.
These days if I were encoding an MP3 I’d use LAME at -V0 setting, letting it lower the bitrate where it can without sacrificing quality. That said, per this test from 2014 that I found as a source on Wikipedia, a 96kbps VBR Opus file is at least as good if not better than an MP3 with -V 5 as the setting on LAME with approximately a 135kbps bitrate.