In my experience with 5 gt turbo shafts and campus ones in drag racing believe it or not campus ones are stronger as there thinner solid shafts, as gt ones have ticker shafts so the shaft is stronger with causes the cv joint to break or spline will snap, when using campus shafts the cv or splines won't break as the shaft will twist as its a thinner solid shaft, but after a while the shaft is so twisted it goes out of balance at high speeds.
The only reasons I can see why gt shafts are ticker in diameter is to do with keeping everything balanced at high speeds