I sure the beta have somethings wrong in the modulation matrix,
i have try the strings presets, and same here,
cpu overload with 5 or 6 notes chord,
try deleting all the macros and mod and watch the result; no overload. one core 15 %
i have try to delete one by one the entry for see if it cause by a kind of modulation, but no,
it's why, i think, something happend with the mod.
W7/I7/Ableton 9.7 64