Datnoids are generally considered slow growers but there are always exceptions. My Datnoids grow steadily at about 3-4 inches per year when young but much less when adults.
Definitely live feeders make them a lot more active and grow faster but I try to use this practice as little as possible just like many here.
NGT's do not grow very fast. My little ones grew from 2 inches to 4 inches in 1 year. Not sure if this is a rule or just my experience with them. Thin Bars are also very sluggish when it comes to growing. I have a 12 inch Thin Bar that was purchased at that size though so I can only hope to grow him even more as the years go by.
Frequency of feeding, type of food and water changes all seem to have an effect on the growth rate.
Ivan