Yeah at 6ft5in some "aasistance" would be needed to really pack it on. I am on the other hand 5ft6in with a medium sized frame so it is possible with high protien diet and training ect for me to get reasonably sizable. I am just getting back into the bb training full on after a 1yr lay off and the diet certainly takes some adjusting too with the increase in meat consumption especially. To be honest its all the cooking that shits me most haha. But I hear what ur saying. Best thing to go for which is what I have been doing is eating alot of egg whites and light fish like talapia which doesnt bloat ur stomach and make eating too much of a chore. Some kinda light cardio before eating helps stimulate my diet, and when I am not too concerned about calories from carbs a small glass of beer or wine helps the appetite as well just before a big meal. I have had friends using equipoise in their cycles that say their appetites go thru the roof, so that might be a solution for u as well, if u havent already tried it.
I tried to find some studies which claimed steroids caused hyperplasia as well as hypertrophy but couldnt find any(I am not saying they dont exist by the way). I did read some interesting research which claimed to back up the GH/slin, IGF-1 mediated hyperplasic effects in muscle, and recommended its use in conjuction with testosterones hypertrophic action for an increased effect, and also to be used in between aas cycles to help keep gains.
Anyway I think you would have to be pretty dedicated(or crazy) to get huge to mess with insulin, but thats just a personal opinion.