@untilde Would it be possible to compile a somewhat similar project in Renoise and Reaper to show and test the CPU differences, so we can test this here and look for problems? Reaper is pretty good with CPU scheduling, but “terrible performance in Renoise” vs. “barely touching 40% CPU in Reaper” sounds like there’s a bug or something else.
Ideally, only free plugins should be used for such a project, so that everyone can test it without buying a bunch of plugin licenses.