I'd say you probably won't manage to make chocolate hard enough to "break a wall". The reason is relatively simple: at it's heart, chocolate is just sugar. While it can be tempered to have various melting points and can be made relatively hard through manipulation of temperature, the result is a relatively fragile crystal structure unsuited to bearing shock. To see just what you could conceivably manage, just look at pure crystalline sugar - I'd wager you aren't going to get anything more durable than that. Adding chocolate to the mix would undermine the resulting hardness as would the introduction of fats.
In the simplest possible way, the hardest "chocolate" would likely be a hard crack stage candy with just enough cocoa to be called chocolate. As you transition towards more common chocolates, especially into the milk chocolates, hardness at any given temperature is going to drop. Of course, if your goal is to break something, it matters little how hard your object in question but rather how much of it you have and how hard you swing it.
