Speedcore, splittercore, extratone, doesn't matter what you call it...just varying degrees of insane tempos, and it's too much past about 250 - 300bpm. Bebop is probably the only kind of incredibly fast music that sounds close to reasonable.
Also, terrorcore, noizecore etc. are a bit out of my listening ability as well.

Breakcore is about my limit. I really like some breakcore stuff actually.