I just found out about Maiko Hakaine. She's a UTAU voicebank that has actual metal screams.

The creator wanted to make the voicebank for Vocaloid originally, but Yamaha said it couldn't be made. So they were like "nah I'd win" and made it in UTAU instead.

It sounds PHENOMENAL HOLY SHIT.

https://www.youtube.com/watch?v=rQAiINVsqTA