I think a lot of depends on if you are planting bare root trees, root pruned trees, fertilized, watered, soil, etc. In poorer soil areas my root pruned trees have flat out left the bare root trees in the dust with all things equal. I believe it's mainly due to a root pruned tree having the advantage of many more feeder roots to scavenge nutrients in less than prime situations. With tubes, water, and fertilizer I have many root pruned Burr Oaks push 6ft tall in two growing seasons. Yes you will have a few freaks that will do better, but 6ft is an attainable number in the masses. I will use a 50/50 mixture of chicken poop and triple 13 every spring when they are first getting going. A fist full spread equally into 3 dibble bar holes is sufficient. If you push the boundaries you will have trees growing so fast that they will not be able to support themselves tubed or not, been there, done that! The first year any tree is planted I water it, this keeps me limited to 500 or so trees because I simply don't have time to water anymore in one evening that I get off per week, life!