I have never heard that rats are more nutritious than mice, but rats are certainly easier to feed an adult snake because of their size. If a pb stays on mice, they need several a week, which people do just fine, but I personally hope I don't have to deal with. The nutritional value of a rodent is largely determined by what the rodent was fed. A healthy snake eats healthy prey.

I am in the same boat though, my girl is on mice still. As soon as she eats the mice I have left, I am trying the switch and hoping she takes to it. You never know though, it's really up to the snake.