The stock conrods are pretty good and have held up well at 300HP. I would put 300HP as the max I would be willing to go as a daily driver on stock internals. Remember that is almost double. The weak point on the rods is the area just below the wristpin that secures it in the piston. There is pleanty of material there for normal and above normal use, to a point. But above 300 you are stressing it too much and need something thicker.