well the generall suggested feeding size is - feed the size of the biggest part of your snake (typically the middle). I personally feed perhaps 8-10% larger than his biggest part when I transition sizes. Meaning when I was feeding rat pups I eventually couldn't notice a lump in him and he was taking them down like breathing. Not that you ever want your snake to struggle with eating but through his body language and the fact that the prey item was no longer making a dent and he always seemed hungry after feeding (rather than retiring to the hide he would dart around or start smelling around the lid of the tank looking for more food) that is when I went to weaned rats (at the time I fed the first one weaned rats were about Icc's biggest girth plus about ten percent. He didn't struggle with it but you could tell it was a more substantial meal for him and he promptly retired to digest after feeding. He's still on weaned rats because they still make a dent though he is seeming hungry again, I fed him two once and he took them gingerly but I don't want to overfeed. I hope somewhere in this rambling is some sort of suggestion or answer. haha