Speed is not only dependent on arrow weight, but on drawlength. However, I wouldn't worry about it if I were him. Speed is completely unimportant. It has never killed an animal and never will. Accuracy is very important, with super sharp broadheads coming in second. I would rate a quiet bow high and consider a forgiving, high brace height to be important for hunting. Speed - it doesn't even make the list of important items, and should never even be considered when choosing a bow.