Well, the Stock Spec has a better on resistance than the Extreme Stock, so it could be a tiny bit "punchier". Plus, according to the specs, the Stock Spec weighs a little less(about a quarter of an ounce) & it can handle mod motors easily, so if you want to go to a much hotter motor later, the Stock Spec will handle it fine, while the Extreme Stock I believe should not run hotter than a 10.5 or 11.5(so running say, an 8.5 in a buggy would not be a good idea, though the Stock Spec can handle it easily)...