I had this same question immediately as well. I was at an expo this weekend trying to predict the growth of my snakes and buying appropriate feeders. Recently I have been feeding my 250-300g snakes 40-60 grams in 2x adult mice. I Bought a bunch of XS rats ~50g ea and a bunch of S rats ~ 60-100g. I almost bought medium rats but was told that that was a substantial size up.
Everything I've read on this site (my main source of knowledge) has indicated 15-20% of avg weight every 3-5 days for growing snakes and 10-15% for adults every 7 days. I was fully anticipating having to feed larger than S rats (60-100g) at around 500 grams.
Is that completely wrong???? I'd really like to see a more comprehensive thread on this, perhaps with shared weight/feeding logs so someone can make a real assessment on enough data to support it.