I respect the fact that you are thinking this out a bit! That's huge. So let me share what little info I know.
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Ruderalis is known for its lack of yield, potency, heavy leaf to bud ratio, small size ect.. Those are just SOME of the traits that breeders spend years breeding out of rudi. Imo, you are much better off crossing the cambodian to rudi then working it to f4, while selecting plants that have the auto gene and that resemble the mom in structure, smell, vigor ect.