The GE Haliade X, smaller but not by a lot, maxes out at 7 rotations per minute, giving a rotor tip velocity in the vicinity of 80m/s. Generally noise considerations mean you don't aim for a tip velocity faster than that, although for a turbine that is only installed in offshore or other uninhabited locations, you might design for a higher tip velocity. Despite some advantages to higher velocity, though, considerations related to erosion caused by high speed impact of dust, water drops and ice particles become an issue long before you'd get to supersonic speeds.