From my experience you are better getting your plants as tube stock.
When they are grown in pots to large sizes it takes them ages to recover when put in the ground.
I have an example now. About five years ago we got a six foot Jacaranda tree in a pot. Cost $70
Two years later I got another one in a six inch pot about a foot high for $12. This tree by the end of summer will be taller than the six footer which has a two year head start.
An exception to this if you get large trees during winter bare rooted as these are not grown in pots but are removed from the ground.
As for the large tree that the original poster wanted, Tasmanian Blue Gums will grow huge at about one metre a year.
Dave.

