The washout (reverse twist) for most helicopters falls between -10 degrees and -16 degrees, where the tip has lower angle of attack than the root. This distributes the average lift across the blade, since the tip is going faster, it needs less angle for the same lift.
The angle could be greater, but the structure of the blade is challenged by the twist angle, in that the stiffness in torsion is weakened by the twist.
Variable twist is coming with the advent of on-blade control, in effect, the movable blade tabs will let the flight control computer select the ideal angel for each segment.