I would cut your crested cactus here
with 2 goals in mind: to keep the cross sectional area of the cut to a minimum, thus reducing the size of the scar on the mother plant; and to remove as much of the normal growth as possible.
There is sometimes a paradoxical effect where removing normal growth only triggers a bunch of branching, and even more normal growth. This tends to be minimized when you try not to leave any normal growth on the mother plant, so as to avoid some great revival down the road.
