My wife can take a replica Lex Steele dildo about 7 inches doggy style before tapping out, but legs up on her back he can go balls deep no problem which is like 9.5 inches.
doggy style up her ass about 5 inches max. Ass up on her side she really likes it deep, about 8 inches before tapping out. But honestly that's about as deep as I can practically go, my wife has really big round athletic ass, you lose about 1.5 inches getting into that thing.