@Sepelion: FWIW, it's actually only onlining 3 cores in note taking mode. Last I checked, simply reading a note-aware document (e.g., KePub, PDF) was enough to enter that "yes, please murder my battery now" mode

. This may have been fixed to only actually trigger on pen hover since.
I've limited us to two cores max in KOReader, and that only when importing metadata, and preloading PDF pages. Otherwise, it's single core, always (which doesn't really matter, as KOReader is heavily single threaded).