Well, now.........
If the stud and the bolt are the same diameter and the same length and are torqued to the same amount they will have the SAME clamping force. It's simple material science. As long as the stud and the bolt are within their elastic limit it doesn't matter what strength they are. The clamping force is determined by the modulus of elasticity of the bolt material and all steels are pretty much the same.

The stud engages more of the threads in the block and you don't get the same wear of the threads because after you turn them in the wear occurs at the nut end. Studs are generally considered to be better but they can be a pain to work around, especially on heads.

R.