being a machinist, i have seen hundreds [if not thousands] of mis-drilled holes in my lifetime.
this is with all types and thicknesses of materials.
i am not afraid of drilling any material. however, the proper machine must be used, as well as the proper drill [bit] for the job, plus having the work piece properly clamped and at 90 degrees from the drill spindle.
This is why I recommend the step drill, keeps the hole centered. The hole for the 5/16" bolt is 11/32", so increase the hole size by steps to 15/32" for the 7/16" bolt. The flexplate material isn't an exotic alloy, just a form of mild steel; so it drills easily with the correct speed.
