As long as you cut off at least 4" from a stock axle, you can re-spline it. If you are going from stock 28 spline to stock 31 spline axles, there will be an increase in strength of app. 33%. Comparing stock 31 to aftermarket 31 is something I have never measured. If you are having trouble with stock axles, it might be wise to go aftermarket. Dutchman will charge you $85.00 a pair for cutting and re-splining for a pair of axles + shipping both ways. I still get a fair amount of axles re-splined to build rear ends in my shop. It all depends on the weight of the car, HP and type of abuse the axle will see to decide whether to use stock axles.