Is a California corner as strong as 3 or 4 stud corner?
Wind damage to the house is not likely to result from bending of the wall studs, even at the corners. Wind-induced damage will occur at the joints between the studs and the soles or caps. 

The exterior sheathing is what will provide stiffness and stability to the entire structure. Use the design that will allow the maximum area of attachment between the corners and the sheathing. The "four stud" corner provides the maximum nailing area on both outside surfaces. 

The "California" corner requires that the sheathing on one of the walls be nailed to the 1.5" narrow edge of a stud. Many framers will not build two-stud or three-stud corners, not because they are more likely to bend, but because they provide insufficient nailing surface.