FWIW, chromoly cages are strong, but they are difficult to add onto easily. Any welding that is done to the cage must be "stress relieved" after the welding is done. I always prefer to use 1018 miled steel rather than the moly tubing with my cages, but that is personal choice. The moly tubes belong on Formula cars and things like that.

Good reading in the Carroll Smith line of books about these subjects. I think Engineer to Win has the explinations of the material science of various grades of steel. Of course all of the Caroll Smiths books are required reading for anyone that is putting a race car on a track.