Among the voicebanks I've collected, almost all of them are Japanese, generally because it's significantly easier to sustain a single syllable at a time when you're a less experienced scream vocalist. So far the only English-focused one I've found is Adrian Exorcism:
http://utau.wiki/utau:adrian
I would highly recommend that any scream bank is used with tn_fnds, with the W200 flag for false chord style if necessary. Fry screams usually sound fine without any flags.
I also have a private beta Japanese CVVC with English extras. Let me know if you'd like this voicebank, though I'm thinking of replacing this bank with an Arpasing one.
I'm trying to work with vocalists in metal communities online to get more proper scream banks recorded, especially since a lot of those guys are more experienced with the style and genre than the typical teenage UTAU user. Hopefully we get to hear some cool results soon!