I never powerfed my bp only because it is unnecessary. It is true that boas appear to be slow grown vs pythons. When my bp refused to eat for 3 weeks, he was visibly losing weight, his skin started to sag and his spine was showing. Granted he would be okay if he continued to refuse for another 2 weeks but he was a skinny noodle for a baby.
My dum boa, on the other hand, had not eaten for 4 weeks. He ate his first 2 meals with me, refused 3, ate another one, and refused last week's meal mostly due to shedding. I am surprised to find him in good health and weight. Barely lost any weight, he looked the same as the day I brought him home, no one would have guessed this bugger did not eat for that long and did not seemed to bothered by it at all.
My other pythons: woma and Children are good feeders. They always wants seconds and might take them if I give in. They and my bp are growing like weeds. My boa shed once, probably grew half an inch since the day I brought him home.
There are studies out there about food intake vs lifespan for humans as well as animals. Ultimately, it will be harder to lose the weight vs to gain it if the animal is overfed. And some animals are hardwired to be opportunistic feeders, like dogs. Most dogs will eat until they vomit or get sick, but that won't stop their desire to keep eating.