>Something I remember is that MP3 spends a disproportionate amount of storage in order to encode frequencies > 16 Khz. This may explain why in some tests, it performs worse in mid-high bitrates (160/192 Kbps), although I don't know the technical details.

I wonder if just straight out filtering them would result in better 160Kbps MP3s, it's not like most people can hear them...