I can't speak the actual material science behind both plastics, but generally PBT is know of a deeper sound, aka "thocc" and ABS higher pitched, aka "clack"

AFAIK (but some one please correct me if I'm wrong) PBT has a higher melting point but the material is still more malleable when solid so it resonates with lower pitches more; ABS on the other hand has a lower melting point but more brittle, hence the resonance with higher pitches

For all factors (but not definitive) aspects of a keyboard that could effect sound, [here's a link]!(https://docs.google.com/spreadsheets/d/15XmznA5T9d4PkfBG0TDS82ou6ihBh0oqr8Aux24SNz0/edit#gid=1460450169)

I could be wrong, but the acoustic different between ABS & PBT should be flipped

You need some GMK Civ in your life

Yo I got it! Ultimate Hacking Keyboard. Indeed looks to be a pain in the ass for all the non regular mods