My first reaction to your reply is the robot response, 10-15% of his body weight a week. I thought about it a little and then I wondered, when does that stop? I don't care if he gets any bigger, I just care that he's healthly. Unless he turns out to be a she, I don't know for sure have just been basing it on size/age and it's easier than typing he/she everytime, there's really no reason to get any bigger, right?
So are you saying continue with one small rat because that will maintain his current weight and keep him healthy?