I start my own Dunstans in air pruning containers. When my dunstan's are 15" tall, they have a very tiny root system and unless you give them lots of supplemental care, they are not field ready. If I properly air prune and plant them after they fill a 1 gal RB2, they generally survive without after care but don't thrive. If I transplant them a second time into a 3 gal RB2, I can get 6' tall trees by the end of the first growing season and they thrive after that.
I know you are not interested in growing them yourself from seed, but this thread should give you a feel for size just by scanning through and looking at the pictures:
http://www.habitat-talk.com/index.p...h-rootmakers-transfered-from-qdma-forum.5556/
Also, keep in mind that height alone is not a good measure of tree quality. A combination of height, caliper, and leaf mass is a much better gauge.
I also concur that Dunstan's are not a good fit for a privacy fence.
One more note on Dunstan: It was originally the name of a patented crossed American/Chinese variety and all "Dunstan's" were grafted. "Dunstan" is also a trade name of Chestnut hill. Most of the trees called Dunstan today are not the grafted clone of the original, but produce from seed. In this context it refers to the trade name of Chestnut Hill.
For a while we heard Chestnut Hill was sending out cease and desist letters to folks selling trees using the name Dunstan. It is probably hard to deal with the little guys as it is like playing whack-a-mole.
Unlike apples and many other trees, Chestnuts are much "truer to seed". That simply means that most of the characteristics we care about are generally preserved even with sexual reproduction. Keep in mind that clonal chestnut trees can not pollenate each other (same clone), so there is some DNA from the male parent.
In general, when I'm referring to Dunstan Chestnuts that I grow in this forum, they are really sons of Dunstans. I purchase nuts from a chestnut orchard that was established with grafted Dunstan trees.
Thanks,
Jack