Dr. New included my daughter in a growth hormone study that she was conducting at Cornell.  It was a few years ago that she started (age 9 and about 4’8").  She received daily injections of growth hormone along with monthly injections of Lupron (to combat her precocious puberty).  I know for a fact that not everyone gets as much growth as my daughter did.  She stopped all treatment at age 12.  She is almost 5’8" (her normal height prediction was 5’9"), and although not "skinny", she is a very nice 140 lbs.  She plays basketball, but other than that, you could always find her laying on the couch reading or watching TV.

For your son, I would be concerned about his weight gain and possible oversupressing.  We had that problem when first diagnosed (at age 5) up until about age 8 when we started seeing Dr. New.  We were originally seeing an endo that only had 2 other CAH patients ever.