interesting topic... the young modulus of any steel, from mild to cro-mo is the same, so essentially, build two frames, using the same tube gauge, one in mild steel, one in cro-mo, they will have the same stiffness and that's the main criteria for handling.
cro-mo has an advantage in ultimate strength but the confusing thing is that the frame should be designed so you will never enter stress levels that get near to ultimate strength, (that's when plastic deformation sets in), but rather stay in the elastic range where all steel perform basically the same.
cro-mo is more resistant then to bend forces but if you desing a frame that acts mostly on push-pull forces like a ducati's triangular ones, there's not going to be much iof an advantage.
Michael Moore from eurospares recomends indeed to use mild steel for home frame building, a lot less headaches with the welding process creating internal strees than with cro-mo's.
TG