Red tails grow slow. They take many years to get to a large size (8ft and 4" in diameter). Retics seem to grow mainly off what you feed them. Get them on rabbits at a early age and you could see 10+ft in the first year. Burms grow slower than retics but stay heavier. Think my friend told me his burms get roughly 6-8ft the first year. And slow down from there. He has a 4 or 5 year old male that is around 12ft. His females are upwards of 15-17ft though by this time. Im personally going for a Burm cause i want a large relaxed snake. One i can hold on the couch and not worry about moving all over the place.