Hehe I bet this burning! I might incorporate those in my routine (not sure if I figure well the 3rd one though). I do not rely on crunch exclusively! Here is my routine : I do chose 7 exercises and do them one after the other to near failure without a break switching very fast between each other, like a huge, very long superset. I took this routine from Corinna Everson, only difference is I swap in new exercises all the time, to keep away from adaptation. Usually 4-5 for the abs and 2-3 for the obliques. Including often plank, side plank, crunches, one dumbbell raise on the side, hip thruster, bent leg raise...etc. It does great for me and new ideas/exercises are always welcome.
Eric