I would say crunchy refers mostly to a sound, but crispy refers to consistency of food (hard but easily breakable). So crispy food is crunchy. About the beef, I wouldn't use crispy or crunchy, i would say crusty (with a nice crispy crust - a layer on the top of the baked or BBQ meet). But of course you can say crunchy if you fry that piece of beef until it is hard. Hope it will help! (BTW i'm not a native speaker)
Crunchy gives me the idea that something will break when pressure is applied, such as nuts or apples. It can only be used for food.
Crispy gives the idea that something is sharp, rigid and dry. For food it gives the idea that it is something cooked, like bacon or potatoes. Crispy can also be used in other ways, for example a crisp morning or a crisp reply.