Well, I would rather have a snake that consistently feeds on small rats all year long than one that eats larger prey for 4 months and then goes off feed for 7-8 months.
The thing to remember is that the snake may be growing, but their metabolism isn't going to increase. So, a 1200 gram snake may be able to fully digest and metabolize a 50-60 gram small rat in 7 days. Can they take a 120g medium rat? yes, most likely. But, because the food was basically doubled, they will need more time to process it. So my opinion is when you start getting into the 100+ gram sizes then it will be time to switch to a 10-14 day feeding schedule. Either way, They are still getting the same amount of prey each month, whether you are feeding 4 X 60g rats, or 2 X 120g rats...