jamesinc;30880 wroteYep they fit the 850 auto gearbox just fine. To my knowledge all the shafts and gearboxes are interchangeable.
I don't think we would be breaking the thinner ones with stock power. I think if you fit an LSD and tuned the car you might get closer to their safe maximum but even then I expect they'd be fine. The knuckles might wear out faster though.
You won't break the shaft but the cv joints can.break as i found out second run up the 1/4mile last Sunday