Just to not sound like a complete asshole… ofc the 25% boost does not depend on bits/kbits, the difference is still 256 vs 320, but I just wanted to emphasize that the expected result is 25% bigger in all terms.

If it helps to imagine, the space needed to store a 256k 5 minutes song will store a 320k 4 minutes song. Then, you are already relying on a quite decent quality beforehand so it’s all extra quality and details.

I usually hear the difference in the high frequency sounds, which is exactly what is otherwise sacrificed in low bitrate compression formats.

FLAC will produce an even better sound, as it’s lossless, but for most songs I couldn’t justify the file size difference.