IMHO actual strength (load before yield and failure) is not really a problem in the sizes and weights used.
It's more stiffness (resistance to bending), which is why frame rails are almost always much taller than they are deep - because the bending will be in a vertical plane. A 4" tall × 1" wide rail is very much stiffer than 1" tall 4" × wide (256 times).
Anything that adds height improves stiffness - such as a roll bar - because it raises the vertical dimension.
For stiffness, there is no practical difference between mild steel and 4130 - no advantage and no weight saving.
