I dont think T.O is doing anything wrong by feeding a burm a small rat at 4 feet! i mean power feeding itself can have its disadvantiges and he just want to let his snake grow moderatly. hey if you let a 8 year old kid eat whatever he wants he is going to end up with serous problems down the line right? so you have to moderate what your child eats. not this my not be a very good analagy but burms are garbage disposals. i bet if you rubbed a rat on a old boot a burm would eat it.
i see that you are building your cage 5 feet tall. realy you dont need that much hight on a cage but let me tell you how it can become handy later on down the line. burms i have found dont like to climb at all once they get bigger and even when they are babys they are dont climb much. i had a big pretty brantch in my burms cage scince day 1 and i have not see my burm cwal on it once! but what you can do is later on down the line you can turn that 1 cage into 2. burms and other large constrictors dont need much "head room" so i am going to split my cage in 1/2 in about a year or so. but ya man keep up the good work with the cage and i would go with medums too. it wont hurt you snake to be in a cage thats a little small for a short peroid of time.
here is my room
and as you can see space is a must!!!!